58 Normentafeln zur Entwicklungsgeschichte der Wirbeltiere. 
to the cloaca. The cloaca (Ol.) is somewhat elongated and the middle third of its floor is in contact, but 
not fused, with the thickened anal plate of ectoderm. The lateral lobes of the liver (L.) extend upward 
above the dorsal wall of the gut. Secondary pouches are forming in large numbers from the walls of the 
main chambers. The anterior lobe, which is obscured in the figure by the sinus venosus, is as yet smooth. 
The gall bladder (@.bl.) now is present as a large ventral pouch the posterior end of which is entirely cut 
off from the median chamber of the liver. The pancreas (Pane.) is connected with the dorsal wall of the 
intestine upon the right side, by an elongated, laterally constricted neck. Three secondary pouches are 
forming from the roof of the pancreas. The Wolffian duct (W.d.) opens into the body cavity anteriorly. 
It is fused posteriorly with the lateral wall of the cloaca near its dorsal boundary. Forty-one mesonephric 
tubules (Mes.t.) are present, the anterior three being exceedingly small. None of the tubules are fused with 
the Wolffian duct, but all except the three anterior overlap this structure to some extent. The pericardial 
cavity (Pe.) is completely cut off from the coelom along the median line by the septum transversum (S.trans.). 
The atrium (At.) now lies almost entirely dorsal to the ventricle (V.) and is connected with it by a distinct 
atrioventricular canal. 
This is the first embryo of the series in which the development of the efferent and afferent 
branchial blood vessels from the aortic arches is indicated. This stage has seemed of sufficient interest to 
A.hyo.eff. Arbr.eff.  Ao.dors. require more detailed illustration than that 
given in the general reconstruction, and for 
this purpose Fig. 14, asomewhat more enlarged 
and slightly diagrammatic view of the same 
structures has been added. The description 
S.ceph. following applies equally to Figs. 14 and ı5 
as the same nomenclature is employed in both. 
The first aortic arch (Ao.a.I) is much reduced 
in caliber, except for a small dilated portion 
\ \ . . . . . 
#4: A.hyo.aff. Ao.vent. A.br.aff. B.cor. which lies immediately under the posterior 
part of the first gill eleft, and which represents 
Fig. 14. 
the position in which the capillary system 
of the spiracular demi-branch will be formed. Anteriorly the first aortic arch joins with its fellow of 
the opposite side forming the base of the sinus cephalicus ($.ceph.). The deep ophthalmic artery (A.oph.) 
arises just anterior to this juncture and runs forward mesial to the optic cup. The second aortic arch 
gives off by two small channels a small and somewhat irregular parallel vessel which represents the 
second or hyoid afferent artery (A.hyo.eff.). Near its ventral extremity this vessel gives off four small 
vascular sprouts which pass into the gill filaments of this arch. The efferent arteries (A.br.eff.) of the third 
and fourth arches are represented by two “T”-shaped vessels springing from the anterior surfaces of the 
respective aortic arches near their dorsal ends. As yet no efferent vessel is represented in the fifth aortic 
arch. The sixth aortic arch is incomplete but vascular sprouts extend upward and downward from the 
ventral and dorsal aorta respectively. The dorsal sprout is joined with the fifth arch by a broad channel. 
From the base of the sixth arch a small vascular sprout passes backward for a short distance over the 
surface of the pericardium. A small vascular sprout also extends backward from the base of the dorsal 
sprout of the sixth arch. The segmental arteries (A.seg.) of the dorsal aorta are established throughout the 
greater part of the trunk region. The vitelline artery (A.vit.) arises by three distinct roots. In all other 
members of the series this vessel arises by two roots and the third or posterior root is represented by a 
slight enlargement on the left side of the aorta. The veins shown in Fig. 13 hardly need description. The 
