198 DISSECTION OF THE DOG 



carotid canal at the apex of the petrous part of the temporal bone, the artery- 

 pursues a course in the cavernous sinus, at first sinuous, but afterwards more 

 direct. Close to the orbital fissure, the artery pierces the dura mater and 

 proceeds to divide into branches which supply blood to the brain. 



The branches at present available for examination are one or two small 

 twigs which anastomose with the middle meningeal artery, and a larger 

 anastomosis with the ophthalmic artery. 



A. mbningea mbdia. — -The middle meningeal artery has been observed 

 to leave the first part of the internal maxillary artery and enter the cranium 

 by the foramen ovale. Within the cranium the artery lies between the parietal 

 bone and the dura mater, occupying a deep groove in the bone. An 

 anastomosis is effected with the internal carotid artery. 



N. petbosus sttpereiciaiis majob. — A very minute nerve, the larger 

 superficial petrosal, should be looked for underneath the semilunar ganglion. 

 Arising from the geniculate ganglion of the facial nerve, it enters the cranium 

 by way of the carotid canal and is joined by the deep petrosal nerve from a 

 plexus surrounding the internal carotid artery. The compound structure thus 

 formed, known as the Vidian nerve (n. canalis pterygoidei [Vidii]), finally 

 joins the spheno-palatine ganglion. 



Dissection. — The cavity of the nose must next be examined. In order 

 to expose the interior of the cavity the skull should be sawn across on a 

 level with the sella turcica, and a sagittal section then made by sawing 

 parallel to and slightly to the side of the median plane. Thus the septum 

 of the nose will be preserved intact on one side of the plane of section. 



Next examine the entrance to the nasal cavity. Observe the area of pig- 

 mented skin surrounding the nostrils. The area is covered with depressed 

 papules, is free from hairs, and in a state of health is moist and cold. 

 The cartilages associated with the nostrils must also be displayed. 



Cabtilagines nasi. — The cartilaginous skeleton of the nose is mainly 

 composed of offshoots from the cartilaginous septum of the nasal cavity. This 

 projects above and beyond the incisive bones and has its dorsal and ventral 

 borders prolonged to such an extent and in such a manner that they meet in 

 the lateral wall of the nasal cavity. In addition to the dorsal and ventral 

 processes of the septum, there is an independent lateral cartilage of roughly 

 triangular form. 



Septum nasi. — The composition of the septum between the two nasal 

 cavities will be disclosed by stripping off the mucous membrane covering it. 

 The septum is partly bony, partly cartilaginous. By far the greater portion 

 of the bony septum (septum nasi osseum) is formed by the vomer and the per- 

 pendicular plate of the ethmoid, but ridges projecting from the frontal and 

 nasal bones play an auxiliary part. 



