164 DISSECTION OF THE DOG 



A. CAEOTTS EXTERNA. — The external carotid artery continues the direction 

 of the common carotid for a short distance along the side of the pharynx, and 

 then forms a curve round the medial and oral sides of the digastric, and between 

 this and the stylo-glossal muscle. The curve brings the artery to a more super- 

 ficial level, and it ends just aboral to the post-glenoid process of the temporal 

 bone by dividing into the superficial temporal and internal maxillary arteries. 

 At no great distance from its commencement, the external carotid artery is 

 crossed laterally by the hypoglossal nerve. Its collateral branches are the 

 lingual, external maxillary, and posterior auricular arteries. 



A. LiNGUAiis. — The lingual artery leaves the external carotid about the 

 aboral border of the digastric muscle and pursues a course towards the side of 

 the tongue, being accompanied by the hypoglossal nerve as far as the border of 

 the hyo-glossal muscle. After crossing the medial face of this muscle, it enters 

 the tongue in company with its satellite vein and the hypoglossal nerve. In 

 order that the full course of the artery may be satisfactorily demonstrated, it 

 is well to reflect the hyo-glossal muscle. The terminal branches of the artery 

 are lost in the substance of the tongue. One collateral branch — the hyoid 

 branch (ramus hyoideus) — should be noted as arising where the lingual artery 

 crosses the hyoid bone, and terminating in the basal part of the tongue. The 

 largest twig of the hyoid branch follows the genio-hyoid muscle towards the 

 tip of the tongue. 



It will be observed that the lingual vein ceases to accompany the artery 

 about the aboral border of the hyo-glossal muscle, and becomes superficial in 

 order to flow into the external maxillary vein. 



A. MAXiLLAEis EXTERNA. — As the external carotid artery crosses the hyoid 

 bone, and as it lies between the digastric and stylo-glossal muscles, it gives 

 origin to the external maxillary artery. Travelling along the dorsal and medial 

 border of the digastric muscle, this vessel reaches the groove between the 

 masseter and digastric muscles at the ventral border of the mandible, and here 

 becomes the facial artery, the course of which has already been traced. 



The collateral branches of the external maxillary artery are : (1) Arteries 

 to the submaxillary and sublingual salivary glands ; (2) branches to the 

 digastric, stylo-glossal, and pterygoid muscles ; (3) the sublingual artery (a. 

 sublingualis), which follows the border of the digastric muscle, and then 

 runs between the mylo-hyoid muscle and the mandible. 



A. AURicuLARis POSTERIOR. — The great or posterior auricular artery leaves 

 the external carotid close to the origin of the digastric muscle and between the 

 muscle and the hyoid bone. The artery, as its name implies, is distributed 

 over the aboral part of the ear, which it reaches by bending round the digastric 

 muscle and running upwards under cover of the parotid gland. 



The following branches should be observed : (1) One or more small vessels 

 spread out over the sterno-cephalic and cleido-mastoid muscles and supply the 

 parotid and submaxillary glands ; (2) a branch of small size — the stylo-mastoid 



