104 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



Transverse Sections of a Six Mm. Pig Embryo 

 Having acquainted himself with the anatomy of the embryo from the study 

 01 dissections and reconstructions, the student should examine serial sections cut 

 in the plane indicated by guide Unas on Fig. 105. Refer back to the external 

 structure of the embryo (Fig. 93), to the lateral dissection of the organs (Fig. 

 95), and having determined the exact plane of each section, interpret the struc- 

 tures seen by comparing with Fig. 105. The various structures may be recog- 

 nized by referring to the figures of sections in the text, and they should be traced 

 section by section through the series as carefully as time wiU allow. Remember 

 that the sections of pig embryos figured here are drawn from the cephalic surface, 

 so that the right side of the section is the left side of the embryo. 



Transverse Section through the Myelencephalon and Otocysts of a 6 mm. Embryo 



(Fig. 106). — As the head is bent nearly at right angles to the body, this section passes length- 



Fourth ventricle- 



' Int. carotid arler 



Dienccplhilotv 



\I yclincephalon 



■Gang, superior n. g 



\)il. cardinal vein 

 ■Gang, acust. n. 8 

 Gang, geniculate n. 7 



Gang, semilunar, n. 5 

 [nl. cardinal vein 



Inl. cardinal vein 



Fig. 106. — Transverse section through the myelencephalon and otocysts of a 6 mm. pig embryo. 

 X 26.5. Gang, acust. n. 8, acoustic ganglion of acoustic nerve, etc. ; Neur. 1-6, neuromeres 1-6. 



wise through the myelencephalon. The diencephalon is cut transversely. The cellular 

 walls of the myelencephalon show a series of six pairs of constrictions, the neuromeres. Lateral 

 to the fourth pair of neuromeres are the otocysts, which show a median outpocketing at the 

 point of entrance of the endolymph duct. The ganglia of the nn. trigeminus, facialis, acus- 

 ticus, and the superior ganglion of the glossopharyngeal nerve occur in order on each side. 

 Sections of the anterior cardinal vein and its branches show on the left side. V^tral to the 

 diencephalon are sections of the internal carotid arteries. 



