442 



DR. 0. F. SONNTAG ON THE 



tricuspid valve. Several small muscle bundles connect the 

 ventricular walls. To the left of the valvular muscles lies the 

 wide, capacious antrum of the pulmonary artery which has no 

 columns! carnea^ The left auricular a])j)endix has subdivided 

 edges, and no columnte carnea?. The left ventricle is thick-walled, 

 and its small cavity is greatly sidxlivided close to its apex by 

 innumerable small muscular bundles. 



The aortic arch gives off the innominate (I. A) and left sub- 

 clavian (L.S.A) arteries and upper three left intercostals, and the 

 former, after giving oft" the left common carotid artery (L.C.A), 

 divides into the right subclavian (E.S.A) and right common 

 carotid (R.C.A) arteries. This arrangement resembles that in 

 many Primates, Carnivora, and Marsupialia. 



The common carotid arteries (text-fig, 18) divide at the level of 

 the upper border of the thyroid cartilage into external carotid 



Text-figure 18. 



The vessels of the head and neck. O.H : omo-hyoid muscle 

 Other letters in text. 



(E.G. A), internal cai'otid (I.C.A), occipital (O.A) and superior 

 thyroid (S.T.A) arteries, and a S3fmpathetic nerve plexus accom- 

 panies the branches. Of these, onl}^ the external carotid requires 

 special mention. 



The external carotid artery (E.C.A) gives oft" a trunk which 

 divides into lingual (L.A) and external maxillary (E.M.A) 

 arteries, and is continued as a trunk which divides into super- 

 ficial temporal (S.T.A) and internal maxillary (I.M.A) arteries. 

 The external maxillary is distributed to the lower lip, parotid, 

 and masseteric regions, and the superficial temporal replaces tlife 

 part wdiich, in most mammals, extends to the inner canthus of 

 the eye. The lingual artery gives off a well-marked branch to 

 the frenal Lamella (text-fig. 19, L.B). 



The subclavian arteries have the usual coui'se and relations, 

 and it is noteworthy that the Annulus of Yieussens suri'ounds 



