File:A treatise on zoology (1900) (14783005022).jpg

Identifier: treatiseonzoolo09lank (find matches)
Title: A treatise on zoology
Year: 1900 (1900s)
Authors: Lankester, E. Ray (Edwin Ray), Sir, 1847-1929 Bather, Francis Arthur, 1863-1934 Goodrich, Edwin S. (Edwin Stephen), 1868-1946
Subjects: Zoology
Publisher: London : A. & C. Black
Contributing Library: Robarts - University of Toronto
Digitizing Sponsor: University of Toronto

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he right and left ductusCuvieri and the hepatic veins join to enter the sinus venosus. Thisleads into a thin-walled atrium, opening into a muscular thick-walled ventricle. There are two sinu-atrial and two atrio-ventricular valves. The ventricle is prolonged forwards into acontractile conns arteriosus, leading to the ventral aorta (Stohr(426), Boas (38-39), Kose (373)). Inside the conns are rows ofsemi-lunar valves (Fig. 69). In the more specialised Teleostei thebase of the aorta is swollen into a non-contractile bulbus, and theconus is reduced to a narrow strip supporting only one row ofvalves (p. 363). As a primiti^^e type of circulation we may take that of aSelachian (Hyrtl, Balfour (27), Hoehstetter (214-15), Dohrn(114), Rabl (336), Parker (314-15)). The median ventral aorta,morphologically a forward prolongation of that longitudinal ventral subintestinal vessel of which the heart itself is a specialisedportion (p. 26), and like that vessel developing from originally paired PISCES
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Ill- - OiS - ■-- .2 S 5~ fe ° 5 ■;.$ ^ T & a, C ,2 J ■^-■e OSS- I =1 ^^ -- ^ C t S K O £ «^ 3 S >uo ° o o ? - a> -e; -3j--^ 2 1° VASCULAR SYSTEM rudiments (Mayer (297fl)),runs forward below thebranchial skeleton (Fig. 71). Itprovides five afferent branchialarteries, the first of whichpasses up the hyoid archto supply its posterior hemi-branch. These afferent vesselsand the efferent vessels arepartially derived from, andreplace, the embryonic com-plete aortic arches, six inmimber, running up the man-dibular, hyoid, and succeedingfour branchial arches. Thepaired rudiments of the dorsalaorta unite to form a singlemedian vessel behind ; but infront they diverge and joinagain below the brain to formin the embryo a completecircle, the circulus cephalicus(Fig. 72). It is this regionwhich receives the efferent orepibranchial vessels. The con-tinuity of the circulus is usu-ally interr

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