DEVELOPMENT OF THE BLOOD VESSELS IN THE FROG. 241 



occipito-vertebral artery arises and runs upwards round the hinder 

 border of the auditory capsule, passing between the glossopharyngeal 

 and pneumogastric nerves. 



Another small branch arises from each aorta just behind the 

 opening of the fourth branchial efferent vessel ; this runs upwards 

 and inwards, and joins the basilar artery of the same side. This is 

 apparently the " vertebral artery " of G-oette.* 



h. The Veins. — We have nothing special to note concerning the 

 veins, except that they are rapidly acquiring definite walls and 

 more uniform calibre, and are losing the lacunar character that 

 distinguished them during the earlier stages. The posterior vena 

 cava is well established as a large median vein lying between the 

 two Wolffian bodies, ventral to the aorta. In front of the Wolffian 

 bodies it leaves the dorsal body wall, and runs forwards and down- 

 wards, lying in a deep groove along the left side of the liver, 

 and joining with the hepatic veins just before reaching the sinus 

 venosus. 



5. General Considerations. 



There are two points that require more detailed consideration 

 at this stage ; firstly, the changes undergone by the vessels of the 

 mandibular and hyoid arches, with which the lingual artery may 

 conveniently be taken ; and, secondly, the establishment of direct 

 communications between the afferent and efferent vessels of each 

 branchial arch at the base of the gills. 



Concerning the vessels of the mandibular and hyoid arches, we 

 may briefly summarise our conclusions as follows : — In each of the 

 four branchial arches, the vessels peculiar to the arch have in Banco 

 temporcma a threefold origin : (1) A pair of lacunar spaces, appearing 

 opposite the level of the external gills, and extending ventrally and 

 dorsally ; the larger space is the first to be formed, it lies in the 

 middle and anterior part of the arch, and it becomes the efferent 

 vessel of the gills of the arch, both external and internal ; the 

 .smaller space appears later, lies in the posterior part of the arch, 

 extends ventrally but not dorsally, gives rise to the afferent vessel 

 of the gills, and acquires connection through the gill capillaries with 



* Goette, A., "Die Entwickclurigsgeschiolite der Unke," Leipzig, 1875, plate xxii,, 

 Fig. 377 a.v. 

 R 



