4S0 



CHORDATA. 



of the mandibular ari'h — a view which has its opponents, who believe these to 

 be a diviJeJ columella 



"The tvmpanic membrane is usually llush with the surrounding; skin or only 

 sliu'hth- below its lewl. In the maninials ii is protected by beinu' placed at the 

 bottom of a deep tube, the cvlo-ii.:! dudil.'rv ii:c.i!iis. The ear conch, a fold of 

 skin supported by cartilage, is also conlined to the mammals. 



The more important vegetative organs of the body are enclosed in a 

 large bodv ca\'itv or i\i'!oin beneath the vertebral column. The cctlom 

 has degenerated in the 

 head and tail region, and 

 in the anmiotes iit the 

 neck as well. The civ- 

 lora is, as development 

 shows, an outgrowth from 

 the primitive digestive 

 tract, an i-iilcnuwlc tpp. f|; ^^ 

 147 and J(-\0, hned with f X il 

 epithelium. Since it 

 arises, as in otJier ccclo- 

 mate animals, by pairec 



IT 



Fig. 534. Fio. 



:;^4. — Ear bones of man ^from \^ icdcrshcini'l. 



A. incus; /f, malleus, ,S", 



Fic. 

 stapes. 



Fig. So^- — Section of vertebrate in abdominal region, a, dorsal aorta; 1", eu-lom; 

 iy, tronad; 1;/, glomerulus; /, iligesti\"e tract; /, liver; ;;/, mesenter\ ; tun, tnuseubir pari of 

 mvtoomes; »m'. its cirlom (mvoea-lrV n. omentum; .s, spinal cord; so. sp. somatic and 

 splancltnic cpithelia; t, ncphridial tubule; ;'»/, ventral mesentery, -.e, \\'oltlian duct. 



outgrowths from the archenterori, it follows that at first the two cavities 

 must be .separated by a partition which also encloses the intestinal tract 

 (hg. 5,1 s)- This partition furnishes the uicsciilcrv which usually supports 

 the intestine dorsally in its whole length frojii the \ertebral column, but 

 ventral of the digestive tract only reaches as far hack as the li\er, so that 

 right and left cocloms unite liehind. Some other organs are also sus- 

 pended in the body cavity by membraires: the testes In' the ;»c,s-();-(7(///;», 

 the ovarv by the iiicsoviirlinii . lit most lishes ami in manv reptiles the 



