A manual of the anatomy of vertebrated animals / by Thomas H. Huxley.

Date:
1871
Catalogue details

Licence: Public Domain Mark

Credit: A manual of the anatomy of vertebrated animals / by Thomas H. Huxley. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    in the earliest embryonic stage only, in other Vertehrata. The blood brought back from the body and from the ali- mentary canal enters a pulsatile cardiac trunk, which runs along the middle of the base of the pharynx, and sends branches up on each gide. The two most anterior of these pass directly to the dorsal aorta; the others enter into the ciliated bars which separate the branchial slits, and, there- fore, are so many branchial arteries. Contractile dilata- tions are placed at'the bases of these branchial arteries. On the dorsal side of the pharynx the blood is poured, by the two anterior trunks, and by the branchial veins which carry away the aerated blood from the branchial bars, into a great longitudinal trunk, or dorsal aorta, by which it is distributed throughout the body. Notwithstanding the extremely rudimentary condition of the liver, it is interesting to observe that a contractile trunk, which brings back the blood of the intestine, is distributed on the hepatic sac after the manner of a portal vein. The blood is collected again into another contractile trunk, which represents the hepatic vein, and is continued into the cardiac trunk at the base of the branchial sac. The corpuscles of the blood are all colourless and nucleated. The skeleton is in an extremely rudimentary condition, the spinal column being represented by a notochord, which extends throughout the whole length of the body, and ter- minates, at each extremity, in a point (Fig. 28). The in- vestment of the notochord is wholly membranous, as are the boundary-walls of the neural and visceral chambers, so that there is no appearance of vertebral centra, arches, or ribs. A longitudinal series of small semi-cartilaginous rodlike bodies, which lie above the neural canal, represent either neural spines or fin-rays (Fig. 28, B, b). Neither is there a trace of any distinct skull, jaws, or hyoidean appa- ratus ; and, indeed, the neural chamber which occupies the place of the skull, has a somewhat smaller capacity than a segment of the spinal canal of equal length. There are no auditory organs, and it is doubtful if a ciliated sac, which exists in the middle line, at the front