352 Dr Barry on the Unity of Structure in 



the subclavian, brachial, coeliac, and renal arteries ; and the inferior cava vein. 

 Malformations occur also, though less frequently, in the nervous system. 

 Many are afforded by the osseous system, as well as by the digestive, respi- 

 ratory, urinary, and generative organs, the organs of sense, &c. 



Meckel attributes the greater tendency in certain parts of the 

 body to malformation, than other parts, to the circumstance, that 

 parts in the " animal series" corresponding to the former, pre- 

 sent normally more numerous varieties than others.* Thus, 

 for example, the anterior or superior extremities are more liable 

 to deviations than the posterior or inferior. This explanation 

 is no doubt the true one. We would add to it only, a reference 

 to the law determining the order in which structures common to 

 a whole class reappear modified in individual development ; for 

 in proportion to the generality of the latter in, the animal king, 

 dom, will their individual reappearance be early and established, 

 and vice versa. As a further proof of this, it may be added, 

 also, that the liability of parts to malformation, is in the direct 

 ratio of their lateness in appearingf. 



The nervous system, as said before, is subject to fewer ano- 

 malies than the vascular, and also than the digestive, generative, 

 and urinary organs ; corresponding to the relative degree of nor- 

 mal variety in these parts in the animal kingdom. This affords 

 a further illustration of the foregoing ; and it may be added, as 

 a proof of the greater universality of the same essential structure 

 in the nervous system of the Vertebrata, that its development is 

 much more pronounced than that of other parts, at an early pe- 

 riod of development.^ 



The coincidence between the presence of ovaria or testes, on 

 the one hand, and of a certain habitus, as well as other circum- 

 stances in various parts of the body, on the other, is sufficiently 

 well ascertained. It is known too, that castration has the effect 

 of neutralizing this genital influence ; rendering males, in general 



* L c. p. 427. 



f Hence if a fundamental and early -formed part be not developed, parts 

 dependent on, and subordinate to it, do not appear. Thus, if the vertebrae be 

 not developed, the ribs do not appear ; and if the ribs are not formed, the 

 sternum also is wanting. Again the lateral portions of the vertebra appear 

 before their spines ; therefore the latter are never present without the for- 

 mer. 



$ See the third paragraph of page 139, in our former paper. 



