240 PROFESSOR MARSHALL AND EDWARD J. BLES. 



the aorta, and from its posterior border, the pulmonary and cutaneous 

 arteries arise (Figs. 13 and 14, A P, AU); the roots of the two vessels 

 being extremely close together, but really independent. The pul- 

 monary artery runs at first downwards and backwards, and then 

 directly backwards along the outer surface of the lung. The 

 cutaneous artery runs upwards and outwards immediately behind 

 the auditory capsule, between this and the head kidney, and divides 

 distally near the surface of the body into anterior and posterior 

 branches, supplying the dorsal surface of the head and body. 



The afferent and efferent vessels of the fourth arch are in direct 

 communication with each other, ventral to the gills, in the same 

 manner as in the anterior arches. "We have found this communication 

 generally though not constantly present in specimens of this age. 



g. The Dorsal Aorta. — The dorsal aortae have undergone but little 

 change since the stage last described. The openings of the efferent 

 vessels of the four branchial arches have been described, and also 

 the origin of the mandibular or pharyngeal artery. In front of this 

 latter the aorta on each side runs inwards rather sharply towards 

 the median plane, and then enters the skull, giving off just before 

 doing so the anterior palatine artery, which runs forward in the 

 mucous membrane of the roof of the mouth as far as the nose. On 

 entering the skull as the internal carotid artery it divides into 

 anterior and posterior cerebral arteries, of which the former runs 

 forwards along the side of the brain, while the latter runs backwards 

 and slightly upwards along the side of the infundibulum, and then 

 backwards along the ventral surface of the brain as the basilar 

 artery (Fig. 13, A B). The arteries of the two sides are connected 

 as before by anterior and posterior infundibular commissures, the 

 anterior or ventral commissure being close to the division of the 

 internal carotid into anterior and posterior cerebral arteries, and the 

 posterior commissure lying in the angle between the infundibulum 

 and the floor of the hind brain. 



Behind the branchial arches the two aortse converge and unite 

 about the level of the hinder end of the head kidneys ; just before 

 their union each aorta is in connection with a glomerulus, which is 

 slightly smaller than in the earlier stages. 



From each dorsal aorta, close to the openings of the third and 

 fourth branchial efferent vessels, and a little in front of these, the 



