122 



THE STUDY OF SIX AND TEN MILLIMETER PIG EMBRYOS 



the head, the shorter tail, the much smaller mesonephric region, the longer 

 umbilical cord and the less prominent segments. The yolk-sac is pear-shaped 

 with long slender yolk-stalk. 



Central Nervous System and Viscera. Dissections show well the form and 

 relations of the organs (Figs. 115, 116 and 117). Directions for preparing dis- 

 sections are given in Chapter VI. 



M etencephalon N. trochlearis 

 Gang. n. 5 \ I M esencephalon 

 Gang. nn. 7 and 8 \ \ I / & oculomotorius 



N. facialis 

 Gang, superior n. 9 

 Gang, jugulare n. 10 

 Gang, petrosal n. 9 



Gang. Froriep 

 Gang, nodos. n. 10 



N. accessorins 

 N. hypoglossus 



Atrium 

 Lung 

 Gang. cerv. 8 



Septum trans-versum 

 Liver 



Mesonephros 

 Gang, thorac. 10 



^nt^ V^M^*' ^ 



Umbilical cord 



Genital eminence 



FIG. 115. Lateral dissection of a 10 mm. pig embryo, showing the viscera and nervous system from 

 the right side. The eye has been removed and the otic vesicle is represented by a broken line. The 

 ventral roots of the spinal nerves are not indicated. X 10.5. n., nerve; r., ramus. 



Brain. Five distinct regions may be distinguished (Figs. 115 and 117): 

 (i) The telencephalon with its rounded lateral outgrowths, the cerebral hemispheres. 

 Their cavities, the lateral ventricles communicate by the interventricular foramen 

 with the third ventricle. (2) The diencephalon shows a laterally flattened cavity, 

 the third ventricle. Ventro-laterally from the diencephalon pass off the optic 

 stalks and an evagination of the mid-ventral wall is the anlage of the posterior 



Diencephalon 



ophthalmic r. n. 5 

 N. opticus 



Maxillary r. n. 5 

 Telencephalon 



Mandibular r. n. 5 

 Chorda tymp. n. 7 



Ventricle 



