168 DISSECTION OP THE DOG 



A. OCCIPITALIS. — One of the two smaller terminal branches of the external 

 carotid which arise about the aboral border of the digastric muscle, the occipital 

 artery crosses the internal carotid artery, the superior laryngeal nerve, the 

 nodose ganglion, and the cranial cervical sympathetic ganglion to reach the 

 surface of the ventral straight muscle of the head, where it is crossed in its turn 

 by the hypoglossal nerve. 



In order to follow the further course of the artery, it is necessary to remove 

 the remains of those muscles attached to the occipital bone which were dissected 

 in connection with the neck. 



In the neighbourhood of the jugular process of the occipital bone the 

 artery makes a curve Avhich brings it to a level with the lateral border of the 

 process. This the vessel follows underneath the posterior straight muscles 

 of the head, thus arriving at a groove between the two nuchal lines of the 

 occipital bone. 



During its course the occipital artery contributes several branches : 

 (1) Numerous small twigs leave it close to its commencement and are expended 

 in the wall of the pharynx and surrounding muscles ; (2) at a point before 

 the occipital artery curves round the jugular process, the condyloid artery (a. 

 condyloidea) takes origin. This vessel divides into several branches, some 

 of which end in the anterior straight muscles of the head. One enters the 

 jugular foramen, while another — which may be regarded as the main continua- 

 tion of the parent artery — enters the condyloid foramen ; (3) while in the 

 groove between the two nuchal lines of the occipital bone, the occipital artery 

 gives origin to the posterior meningeal artery (a. meningea posterior), which 

 at once enters the cranium by a neighbouring foramen ; (4) the cerebro-S'pinal 

 artery (a. cerebro-spinalis) enters the vertebral canal by the intervertebral 

 foramen of the atlas, and, joining a branch from the vertebral, forms the 

 basilar artery of the brain. 



A. CAROTis INTERNA. — Like the occipital, the internal carotid artery is 

 small. From its origin immediately aboral to that of the occipital artery, the 

 internal carotid runs in a dorsal and oral direction within the occipital artery 

 and the hypoglossal nerve and lateral to the superior laryngeal nerve and the 

 nodose ganglion. After crossing the ventral straight muscle of the head, the 

 artery enters the carotid canal and so gains the interior of the cranium. 



V. jUGiTLAEis INTERNA. — In the region of the basilar part of the occipital 

 bone, the internal jugular vein is formed by the union of the inferior cerebral, 

 the occipital, and a number of small veins. By crossing the side of the pharynx 

 the vein gains the ventral border of the common carotid artery and so travels 

 down the neck. 



Dissection. — Make a longitudinal incision close to the middle line through 

 the wall of the pharynx and the soft palate. 



Palatum molle. — In the dog the soft palate forms a long and broad 



