1867.] 251 [Wyman. 



yond it, in the human body, the bodies of the vertebra3 first ossified, 

 viz., tho«e in the middle, are the largest, and from these the column of 

 bodies gradually tapers to the head and coccyx. It is only towards 

 the end of toetal life that the lumbar vertebrje assume larger propor- 

 tions. Fifthly, a resemblance analogous to that which exists between 

 the opposite ends of the nervous system and of the vertebral column, 

 can also be traced in the intestinal canal. Oken first maintained the 

 idea that the oral and anal portions of this canal repeat each other. 

 Notwithstanding the ridicule which has been directed to this view of 

 his, fairly examined, it will be found to have, underlying it, at least 

 the semblance of a truth. The two opposite ends agree in this, that 

 in the embryos of all air-breathing animals there is developed from the 

 abdominal side of each end of the straight symmetrical intestine a sac ; 

 that in front forming the lung, and that behind the allantois, and each 

 opening into the intestine by a narrow neck. The allantois as well as 

 the lung is a respiratory organ, but it is not justifiable to cite a function 

 as an indication of homology. The correspondence between the two 

 ends of the canal is still further, but less clearly, indicated in the sub- 

 sequent division of them, the fore end into mouth and nostrils, or 

 respiratory and digestive portions, and the hind into anal and genito- 

 urinary portions, and still further by the develojiraent of the tongue 

 on the f oor of the mouth, and of the male organ on that of the geni- 

 tal portion of the intestine. In most mammals the genito-urinary por- 

 tion bee mies wholly separated from the digestive, while the respiratory 

 does not. Nevertheless in the embryo the first retains its connection 

 for a ce.-tain time, as is permanently the case in the birds and reptiles. 

 The 1 lost striking flicts bearing upon the idea of fore and hind sym- 

 metry are to be found in the development of the limbs. Von Baer 

 has described the phases which the limbs assume, as also their attitudes 

 as they advance towards their permanent condition. AVe have traced 

 these successive positions in several embryos, and from them the fol- 

 lowing description is drawn. The limb-buds, when first formed, are 

 simply tegumentary outgrowths, and project at right angles from the 

 sides of the body in the form of half oval discs. As they increase in 

 length they become divided into a somewhat flattened, disc-like end, 

 which becomes the future hand or foot, and a pedicle which connects 

 this with the trunk. This pedicle is transformed into the fore arm and 

 leg, and partly into the arm and thigh ; the remaining portions or 

 these la^t, when developed, result from a still further outgrowth from 

 the body which takes place at a later period. In the second stage the 

 limbs ari each bent to an angle at a point near the trunk, so that 

 their emls are directed dowuAvards, and what were previously the under 

 sides of the disc-like hands and feet (the body being supposed to be 

 horizontal), have now become vertical and face iuAvards ; they are the 



