HEAD AND NECK OF THE HORSE 145 



section (page 131). To reach the brain, in which it is finally 

 distributed, the artery passes through the ventral petrosal and cavernous 

 sinuses and through the connecting link between them. While tra- 

 versing these sinuses, the artery forms an S-shaped curve, after which it 

 pierces the dura mater on a level with the infundibulum. A transverse 

 vessel (a. intercarotica) lies within the intercavernous sinus and connects 

 the internal carotid arteries of the two sides of the head. 



The termination and distribution of the internal carotid artery will 

 be examined in connection with the dissection of the brain. 



Meningeal arteries. — The dura mater is supplied with blood by 

 the anterior, middle and posterior meningeal and the condyloid arteries. 

 The middle meningeal artery (a. meningea media) arises from the first 

 part of the internal maxillary, and enters the cranium by the foramen 

 spinosum. Its branches occupy grooves on the cerebral surface of the 

 parietal and temporal bones. The posterior meningeal artery (a. 

 meningea posterior) is the branch of the occipital that follows the 

 sinuous groove on the mastoid part of the temporal bone and enters the 

 cranium by traversing part of the temporal meatus. Slender anasto- 

 moses occur between this artery and the preceding. The anterior 

 meningeal artery (a. meningea anterior) is a small branch of the 

 anterior cerebral. In addition to supplying the dura mater of the 

 anterior cerebral fossa, it assists in the formation of a network of vessels 

 in the ethmoidal fossa. The condyloid artery (a. condyloidea) furnishes 

 meningeal branches that enter the cranium by the jugular and hypo- 

 glossal foramina. 



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 on one side of the head. 



The nasal cavity (Cavum nasi). — Tlie nasal cavities are elongated 

 passages extending from the nostrils to the choanse (posterior nares), by 

 which they communicate with the pharynx. All the facial bones, with 

 the exception of the mandible and the hyoid, take part in the formation 

 of their boundaries ; and the palatine, maxilla and incisive bones 

 separate them from the mouth. 



Cartilages of the Nose (Cartilagines nasi). — The cartilaginous 



skeleton of the nose consists of the cartilage of the nasal septum 



(cartilago septi nasi), and certain smaller cartilages. The septal 



cartilage is a wide, elongated plate that may be regarded as an un- 



ossified anterior prolongation of the perpendicular plate of the ethmoid. 



Its thick and rounded lower border fits into the groove of the vomer 

 10 



