SPECIAL ANATOMY. 123 



muscles of the external ear. To the conchial cartilage 

 run the extrinsic auricular muscles ; those anteriorly 

 situated are the attrahentes, and are attached to the zygo- 

 matic process and to the parietal ridges. The retrahentes 

 are attached to the liganientum nuchse, and by areolar 

 tissue to the muscles situated externally to the muscles 

 of the poll. The adductor muscles run from the crest of 

 the occiput ; debility of these causes the animal to 

 become " lop-eared." Parotideo auricularis is the abductor ; 

 it runs from the external part of the base of the conchial 

 cartilage, to become attached below to the external surface 

 of the parotid gland. It is not directly subcutaneous, but 

 covered by a thin layer of panniculus. Around the base 

 of the conchial cartilage is a quantity of fat, which facili- 

 tates its movements. The common integument covering 

 the external surface of this cartilage at its upper third is 

 reflected over its margin at the meatus auditorius exter- 

 nus (or slit) to line the conchial and annular cartilages, 

 and the external auditory canal, at the bottom of which it 

 covers the external surf ace of membrana tympani. It is 

 very fine and at the internal surface of the conchial 

 cartilage presents long hairs which seem to close up 

 the external opening ; they serve to prevent the ingress of 

 foreign matters. More internally it presents sebaceous 

 glands modified for the production of the cerumen or wax 

 of the ear, ceruminous glands. We notice that the external 

 ear of the ass is more developed than that of the horse. 

 The external ear receives blood by the anterior and pos- 

 terior auricular branches of the external carotid artery ; 

 the latter sends a large branch, middle auricular, to the in- 

 ternal surface of the conchial cartilage. The nerves of the 

 external ear are derived from the facial, fifth cranial, and first 

 cervical nerves. 



The inferior maxilla must now be partially removed 

 by incision through the interdental space and through its 

 neck after masseter externus has been separated from its 

 inferior attachment, and thrown upwards over the zygo- 

 matic spine. By removing the piece of bone thus separated 

 we expose the anterior attachment of digastricus inf eriorly, 

 and above tbis we cut through the attachment of 



Mylo-hyoideus, which arises from the alveolar ridge at 

 the superior part of the internal surface of the inferior 

 maxilla. Its fibres run towards the centre of the inter- 



