160 



STUDY OF PIG EMBRYOS. 



of every embryo, and make, with the aid of the camera lucida, an exact dr'awing 

 of every embryo before he cuts it into sections. He will soon learn that such a 

 drawing is almost indispensable for the interpretation of the sections. 



Under the following paragraphs, embryos of 12, 15, and 20 mm. are figured 

 and described from specimens which have been hardened in Zenker's fluid and 

 preserved in alcohol. The description of these stages will be sufficient to enable 

 the student to understand any of the embryos he is required to study. 



Ven. Md. Au. 



A.L. 



M.L. 



P.L 



Fig. 99. — Pig Embryo of 10 mm. 

 A.L, Anterior limb. Au, Auditory, or first gill cleft. C.S, Cervical sinus. Md, Mandibular process. 

 M.L, Milk-line. Mx, Maxillary process. N, Nasal pit. Op, Eye. P.L, Posterior limb. Seg, Mus- 

 cular segment. Um, Umbilical cord. Ven, Floor of fourth ventricle (medulla oblongata). X ^ diams. 



Pig Embryo of 10 mm. (Fig. 99). — The head, which is very large, in compari- 

 son with the body, forms as a whole nearly a right angle with the back, so that 

 the dorsal outline of the head forms a distinct though rounded angle with that of 

 the back; this angle marks the position of the neck bend, and corresponds to the 

 junction of the brain with the spinal cord. The neck bend is one of the most 

 marked and distinctive characteristics of the mammalian embryo, being much 



