Applied Anatomy of the Maxillofacial and Mandibular Regions of Indian Mithun (Bos frontalis) and its Clinical Significance in Regional Anesthesia

Mithun (Bos frontalis) is also known as gayal or ‘Cattle of Mountain’ is a rare bovine species living under free-range conditions inside the tropical rainforest ecosystems of India, Bangladesh, Bhutan, China and Myanmar (Mondol et al., 2004). It is a unique animal having a massive body, with characteristic ‘white stockings’ on their stout legs. This animal efficiently converts grass, forage, tree leaves as well as various agricultural by-products into highly nutritious meat (Mukherjeeet_al2019). Mithun plays a vital role in the socio-economic and cultural life of the local tribal population in the northeast region of India (Mondol et al., 2007; Shisode et al., 2009; Mondal et al., 2014). The regional anatomy is one of the major foundations of clinical and surgical practice as it enables the clinician/surgeon to visualize the details of the structures relevant to the case at hand (Dyce et al., 1996). The knowledge of the regional anatomy of the head is crucial as it has to coordinate the body, deglutition, olfaction and defense (Dyce et al., 1996). Numerous investigations have been done on the regional anatomy of the head region of the domestic and wild animals including ox, horse, sheep, goat, dog, pig and camel (Dyce et al., 1996; Hall et al., 2000; Onar et al., 2001; Olopade and Onwuka, 2005; Karimi et al., 2011; Choudhary et al., 2016, 2017, 2019).
        
It has been reported previously that the infraorbital nerve and mental nerve pass from the infraorbital foramen and mental foramen, respectively (Getty, 1975; Ghosh, 2012). In an emergency situation that requires surgical intervention, it is very easy to locate this region as a topographical landmark for quick and easy anesthesia to block the infraorbital and mental nerves. There is no previously reported information on the applied anatomy and clinical significance of the maxillofacial and mandibular region of mithun. Therefore, the present study has been designed to provide information on clinically important parameters and landmarks for regional anesthesia on the maxillofacial and mandibular regions in mithun.

The study was conducted on the maxillofacial and mandibular regions of twelve (n=12) adult mithun of either sex (n=6, male and n=6, female). The samples were collected from the head region of naturally died mithun from different parts of the Mizoram and Nagaland state of India from April 2019 to March 2020. All the procedures involving sample collection were conducted as per the Institutional Animal Ethics Committee (IAEC) which is under Committee for the Purpose of Control and Supervision of Experiments on Animals (CPCSEA), Ministry of Environment, Forest and Climate Change, Government of India for the College of Veterinary Sciences and Animal Husbandry, Selesih, Aizawl, Mizoram, Aizawl, Mizoram.
        
After collection, the samples were processed by the hot water maceration technique (Choudhary et al., 2013a,b). The skulls and mandibles were kept in 4% hydrogen peroxide for three days and further sundried for seven days (Choudhary et al., 2020a,b). The present study was carried out in the Department of Veterinary Anatomy and Histology, College of Veterinary Sciences and Animal Husbandry, Selesih, Aizawl, Mizoram. The radiograph of the mandible was carried out by the Siemens X-Ray machine (500 mA) at the Department of Veterinary Surgery and Radiology, College of Veterinary Sciences and Animal Husbandry, Selesih, Aizawl, Mizoram.
        
Altogether a total of twelve measurements were taken in the maxillofacial and mandibular regions of mithun by using digital vernier caliper (Resolution 0.01 mm or 0.0005 inches: Accuracy +/- 0.03 mm) and the results were expressed as mean±standard deviation (SD). The parameters taken in maxillofacial and mandibular regions are delineated below and revealed in Fig 1-4.
 

 

 

 

 
A.   Facial tuberosity to the infraorbital foramen: It was measured the level of most lateral bulging of facial tuberosity to mid-level of the infraorbital foramen.
B.  Infraorbital foramen to root of alveolar tooth: It was measured from the mid-level of the infraorbital foramen to the alveolar root of the superior first premolar tooth.
C.  Lateral alveolar root to mental foramen: It was measured from the lateral extent of the alveolar root of the third inferior incisor tooth to the mental foramen.
D.  Mental foramen to the caudal mandibular border: It was measured from the level of the mental foramen to caudal border of the ramus of the mandible.
E.     Maximum mandibular length: It was measured from the level of the rostral extremity of the alveolar root of the central inferior incisor tooth to the transversal plane at the level of the caudal border of the mandible.
F.    Maximum mandibular height: It was measured from the highest level of the coronoid process perpendicularly to the ventral mandibular margin of the mandible.
G. Condylar process to the height of mandible: It wasmeasured from the condylar process to the maximum height of the mandible.
H.  Condylar process to the ventral margin of the mandible: It was measured from the highest level of the condylar process to the ventral mandibular margin.
I.     Mandibular foramen to the horizontal plane at the level of the ventral margin of the mandible: It was measured from the ventral limit of the mandibular foramen to the horizontal plane at the level of the ventral margin of the mandible.
J.    Mandibular angle to mandibular foramen: It was measured from the extreme caudal border of angle of the mandible   to mandibular foramen.
K.    Caudal border of the mandible to below mandibular foramen: It was measured from the caudal border of the mandible to the vertical line produced by a description of measurement of mandibular foramen to the ventral margin of the mandible.
L.    Mandibular foramen to the cranial border of the mandible: It was measured from the mandibular foramen to the cranial border of the mandible.
 
All the above parameters of the maxillofacial and mandibular regions of mithun were obtained. All the measurements obtained were analyzed by routine statistical analysis (Snedecor and Cochran, 1994) and Student ‘t’ test by the Statistical Package for the Social Sciences (IBM, SPSS, 20.0 version) program.

The infraorbital foramen, mandibular foramen and mental foramen on the medial and lateral surface of the maxillofacial and mandibular regions have been shown in Fig 1-3. The measurement points taken to determine the topographic and morphometric location of the mental foramen have been shown in Fig 2. The infraorbital foramen was small, elliptical and was located at the level of first superior premolar tooth in mithun (Fig 1). The facial tuberosity was located dorsally to the third superior premolar tooth in mithun. The mandible of mithun showed oval mental foramen with unossified mandibular symphysis. The results of the measurements have been listed in Table 1.
 

        
All the obtained parameters were significantly (P<0.01** and P<0.05*) higher in males as compared to the females of mithun. The present study revealed that all the obtained parameters showed a significant statistical difference (P<0.01** and P<0.05*) between the males and females of mithun, however, considering from the practical point of view, these differences were meager.
        
In the present study, the facial tuberosity of mithun was located above the third superior premolar tooth which has also been reported in ox (Getty, 1975), chital (Kumawat et al., 2014) and blackbuck (Choudhary and Singh, 2016), however, the facial tuberosity of the Madras Red sheep was prominent and placed at the level of fifth cheek tooth (second superior molar tooth) (Sundaram et al., 2019). The distance between the most lateral bulging of the facial tuberosity to the infraorbital foramen and from the latter to the root of the alveolar tooth directly ventral to it was 4.51±0.02 cm and 2.95±0.01 cm in males; 4.46±0.02 cm, 2.92±0.01 cm in females of mithun (Table 1). However, the same parameter was reported as 1.6-1.8 cm and 1.3-1.6 cm in WAD goats (Olopade and Onwuka, 2005); 1.85±0.14 cm and 1.75±0.19 cm in black Bengal goat (Uddin et al., 2009); 1.92±0.14 cm and 1.64±0.14 cm in Iranian native goats (Monfared et al., 2013); 2.06±0.14 cm and 1.13±0.11 cm in GVD goat (Kataba et al., 2014); 2.8 cm and 2.5 cm in Iranian native cattle (Monfared 2013), 2.37±0.00 cm and 0.72±0.00 cm in blackbuck (Choudhary and Singh, 2015a) and 6.00 cm and 1.50 cm in buffalo of Egypt (Farag et al., 2017). In one more study, the distance between the infraorbital foramen to the root of the alveolar tooth was 1.36±0.06 cm in males and 0.96±0.09 cm in females of chinkara (Din et al., 2020).
        
The infraorbital nerve is a continuation of the maxillary branch of the fifth cranial nerve after it enters the infraorbital canal (Farag et al., 2017). It emerged on the face as a flat band through the infraorbital foramen, where it was covered by the levator nasolabialis muscle and soon divided into several rami that distributed to the nasal region and maxillary lip (Farag et al., 2017). The infraorbital foramen was small, elliptical and located at the level of first superior premolar tooth in mithun as reported earlier in chital (Kumawat et al., 2014) and blackbuck (Choudhary and Singh, 2016). However, the same foramen was located dorsally to the second premolar in red Sokoto (Maradi) goats (Olopade and Onwuka, 2007).
        
The extraoral infraorbital nerve block (Fig 5) can be achieved by injecting anesthetic drugs approximately 3.00 cm in mithun above the root of superior first superior premolar tooth in the infraorbital foramen. However, the same nerve can be achieved by injecting anesthetic drugs approximately 1.00 cm in barking deer and 1.80 cm in sambar deer at the level given above (Keneisenuo et al., 2020). The infraorbital nerve block is used in the surgical interventions related to the upper lip, nose and skin supplied by the infraorbital nerve.
 

        
The above-recorded parameters were of clinical importance because the facial tuberosity is remarkable even in live animals providing a clear guide for tracking the infraorbital nerve and its desensitization during the manipulations in the skin of the upper lip, nostril and face at the level of the infraorbital foramen.
        
The distance between the lateral alveolar roots of the third inferior incisor tooth to the mental foramen was 5.29±0.02 cm in males, 5.26±0.01 cm in females of mithun (Fig 2) which was an important landmark for achieving the location of the mental foramen nerve for the regional nerve block in mithun. In contrast, it was 2.54 cm in adult cows of Pakistan (Shahid and Muhammad, 2001), 3.81 cm in adult buffalo of Pakistan (Shahid and Muhammad, 2001), 1.60±0.22 cm in WAD goat (Olopade and Onwuka, 2005); 2.00±0.3 cm in red Sokoto (Maradi) goats (Olopade and Onwuka, 2007); 2.5 cm in Iranian native cattle (Monfared 2013), 2.45±0.00 cm in blackbuck (Choudhary and Singh, 2015a); 4.32±0.41 in donkey (Mohamed and Fathy, 2015), 4.0±0.12 cm in crossbred cattle (Rajathi 2015) 9.22±0.05 cm in dromedary camel (Choudhary et al., 2016), 3.57±0.04 cm in local pig of Mizoram (Choudhary et al., 2019) and 1.58±0.29 cm in males; 1.25±0.19 cm in females of chinkara (Din et al., 2020).
        
The mental nerve is a branch of the mandibular alveolar nerve that emerged via the mental foramen and divides into three branches below the depressor angulioris muscle (Farag et al., 2017). These branches distributed to the skin of the chin as well as the skin and mucous membrane of the lower lip (Farag et al., 2017). The extraoral mental nerve block (Fig 5) can be achieved by injecting anesthetic drugs approximately 5.30 cm in mithun from the lateral extent of the alveolar root of inferior third incisor tooth into the mental foramen. However, the same nerve block can be achieved by injecting anesthetic drugs approximately 2.80 cm in barking deer and 3.00 cm in sambar deer at the level given above (Keneisenuo et al., 2020). Choudhary et al., (2020c) also mentioned in goats of Mizoram that the infraorbital nerve block can be achieved extraorally by injecting anesthetic drugs approximately 1.4-1.5 cm above the root of the second superior premolar tooth in the infraorbital foramen. The mental nerve block is useful for desensitizing the lower lip during its surgical interventions.
        
The maximum distance from the mental foramen to the caudal border of the ramus of the mandible was 31.30±0.04 cm in males, 31.27±0.03 cm in females of mithun, while the same parameters were 13.43±0.08 cm in blackbuck (Choudhary and Singh, 2015b); 11.69±0.40 cm in black Bengal goat (Uddin et al., 2009); 13.74±0.18 cm in Mehraban sheep (Karimi et al., 2011); 9.26±0.49 cm in GVD goat (Kataba et al., 2014); 32.12±0.16 in dromedary camel (Choudhary et al., 2016); 15.23±1.46 cm in Barbados black belly sheep (Mohamed et al., 2016); 11.8±0.89 cm in black Bengal goat (Poddar et al., 2018), 12.38±1.52 cm in Abaza goats (Dalga 2019) and 18.47±0.01 cm in local pig of Mizoram (Choudhary et al., 2019).
        
The mandibular length and height was 37.10±0.06 cm, 21.25±0.02 cm in males and 37.06±0.05 cm, 21.19±0.04 cm in females of mithun, respectively. Whereas, the same mandibular parameters were 12.00±0.89 cm, 6.90±1.09 cm for WAD goats (Olopade and Onwuka, 2005); 14.21± 0.98 cm and 8.83±0.40 cm in black Bengal goat (Uddin et al., 2009); 11.24±0.52 cm, 6.64±0.44 cm in GVD goat (Kataba et al., 2014); 16.53±0.12 cm, 10.69±0.02 cm in blackbuck (Choudhary et al., 2015b); 42.98±0.62 cm, 22.58±0.28 cm in dromedary camel (Choudhary et al., 2016), 31.20±1.30 cm, 22.75±1.13 cm in donkey (Mohamed and Fathy, 2015), 25.02±0.09, 10.54±0.07 cm in local pig of Mizoram (Choudhary et al., 2019) and 14.18±0.48 cm, 8.21±0.33 cm in males; 12.93±0.96 cm, 7.33±0.50 cm in females of chinkara (Din et al., 2020).
        
The distance between the condylar process to the height of the mandible, condylar process to the ventral margin of the mandible was 5.22±0.01 cm, 15.30±0.04 cm in males and 5.18±0.01 cm, 15.19±0.03 cm in females of mithun. However, the same parameter has been reported as 3.09±0.00 cm, 7.57±0.02 cm in blackbuck (Choudhary et al., 2015a).
        
The distance between a vertical line drawn downward from the caudal border of the mandible (I) and the vertical line drawn from mandibular foramen downwards (F) was (G) 3.62±0.01 cm in males, 3.60±0.01 cm in females of mithun (Fig 3). However, the same parameter was observed as 1.85±0.01 cm in blackbuck (Choudhary et al., 2015a) and 1.54±0.08 cm in males and 1.60±0.14 in males of chinkara (Din et al., 2020).
        
The mandibular nerve is a branch of trigeminal and enters the mandibular foramen on the medial aspect of the vertical ramus of the mandible and emerges through mental foramen on the lateral aspect of the mandible. The mandibular nerve block (Fig 5) is used to anesthetize the mandibular nerve during the clinical examinations and surgical procedures involving the alveoli and teeth of the lower jaw in animals (Lahunta and Habel, 1986). The distances from the mandibular foramen to the ventral margin of the mandible, caudal border of the mandible to the level of the mandibular foramen, mandibular foramen to the border of mandibular angle were 7.75±0.03 cm, 3.62±0.01 cm, 6.71±0.02 cm in males; 7.69±0.02 cm, 3.60±0.01 cm, 6.67±0.01 cm in females of mithun (Fig 3). Whereas, the same parameters were recorded as 4.18±0.01 cm, 1.36±0.01 cm, 3.07±0.00 cm in blackbuck (Choudhary and Singh, 2015a); 8.84±0.08 cm, 5.88±0.05 cm, 8.29±0.07 cm in dromedary camel (Choudhary et al., 2016) and 4.56±0.01 cm, 3.81±0.00 cm, 4.84±0.01 cm in local pig of Mizoram (Choudhary et al., 2019). Equivalent Fig for WAD goats of Nigeria were 1.57±0.44 cm, 2.58±0.34 cm for the caudal border of the mandible to below mandibular foramen and the mandibular foramen to the ventral margin of the mandible (Olopade and Onwuka 2005). The distance between mandibular foramen and the ventral margin of the mandible was 3 cm and 1.5 to 2 cm in horse and dog, respectively (Hall et al., 2000). The mandibular nerve is useful during the treatment of the injuries related to the lower incisors and premolar teeth. i.e. dental extraction, tumors etc. An extraoral mandibular nerve block can be achieved by injecting anesthetic drugs approximately 7.75 cm in mithun from the horizontal plane at the level of the ventral margin of the mandible to the ventral limit of the mandibular foramen. However, the same nerve block can be achieved by injecting anesthetic drugs approximately 2.5 cm and 5.0 cm in barking deer and sambar deer, respectively at the level given above (Keneisenuo et al., 2020).
        
The distance between the mandibular foramen to the cranial border of the mandible was 3.50±0.02 cm in males and 3.45±0.02 cm in females of mithun; however, the same parameter was recorded as 5.00±0.55 cm in cattle (Nazih and El-Sherif, 2018). An intraoral mandibular nerve block can be achieved by injecting anesthetic drugs approximately 3.5 cm in mithun from the cranial border of the mandible to the mandibular foramen.
        
The applied anatomical data created from the mentioned parameters described in the present investigation were not reported earlier in the mithun, which have great clinical significance and may be used as a landmark for tracing the infraorbital nerve, mental nerve and mandibular nerve desirable for their desensitization during any type of surgical procedure at the level of the specific foramen.

It can be concluded that the measurements obtained from the present study would be useful for the clinicians to locate the site for infiltration of the anesthetic drugs for the nerves of head region and can aid the veterinary practitioners in treating the head injuries related to mithun. Further, the data generated from the present study will be beneficial in future endeavors involving applied research works leading towards the massive improvement of the livestock sector.

The authors are thankful to the Vice-Chancellor and Director of Research, Central Agricultural University, Imphal for Sanctioning the Intramural Research Project (IRP). The authors are also grateful to the Dean, College of Veterinary Sciences and Animal Husbandry, Central Agricultural University (I), Aizawl, Mizoram for providing all the necessary facilities to carry out present research investigation.