OF THE GROWTH AND DECREASE, &C. 405 



be regarded as the grandest effect of the nisus forma- 

 tivus, arid at which it arrives by gradual changes or, if 

 we may so speak, metamorphoses, from a more simple 

 to a more perfect form.* 



642. The formation of human bone f begins, if we are 

 not deceived, in the seventh or eighth week. First of 

 all, the osseous fluid forms its nuclei in the clavicles, 

 ribs, vertebrae, the large cylindrical bones of the ex- 

 tremities, the lower jaw, and some other bones of the 



* Hence, as I have remarked in another place, (Nova Litter aria Goettingen- 

 sia, a. 1808. p. 1386) human monsters are sometimes met with so strongly 

 resembling the form of brutes, because the nisus formativus, having been dis- 

 turbed and obstructed from some cause or other, could not reach the highest 

 pitch of the human form, but rested at a lower point and produced a bestial 

 shape. O n the contrary, I have never once found among brutes a true example 

 of monstrosity, which, by a bound of the nisus formativus, bore any analogy 

 to the human figure. 



For fuller information in regard to the resemblance of the very early human 

 embryo to the larvae of reptiles, and in some measure to the foetuses of qua- 

 druped mammalia, consult after Harvey, De generat. animal, p. 184, 235 sq. 

 London. 1651. 4to. Grew, Cosmol. sacr. p. 37, 47. Lister, De humoribus. 

 p. 444. and others, especially Autenreith, Observat. ad histor. embryon.facien- 

 tium. P. i. Tubing. 1797. 4to. Fr. Meckel, both Auff'dtz. zur menschl. u. 

 vergleich . an at. p. 277 sq. and Beytr'ag. zur vergleich. anat. p. 63, and else- 

 where. And Const. Anast. Philites, 1. c. 



T I say of human bone; for in the incubated chick it commences much 

 later, — at the beginning of the ninth day, which corresponds with the seven- 

 teenth week of human pregnancy. 



Obse rvations, therefore, made on the incubated chick, must not be hastily 

 applied to the formation of the human embryo, — an error committed by the 

 great Haller himself, who asserted decidedly that what he had demonstrated 

 in regard to the incubated chick, was equally applicable to other classes of ani- 

 mals and to man himself. 



This opinion subsequently gained so much ground, that some physicians, who 

 endeavoured to settle the forensic disputes respecting premature labour, de- 

 duced their ar guments from this hasty comparison of the periods of incubation 

 with those of human pregnancy. Vide V. c. Hug. Marreti, Consultation au 

 sujet d'un enfant, <Vc. Dijon. 1768. 4to 



