100 J. B. JOHNSTON 



PIG EMBRYOS 



The ganglion of the nervus terniinalis (ganghon terminale) is 

 distinguishable in the 9 mm. pig and the nerve has been seen in 

 all the specimens examined of various stages up to 53 mm. It 

 is most conspicuous in embryos of 15 to 25 mm. after which it 

 seems to grow smaller. It was not seen in the later stages exam- 

 ined, namely, of 74 mm. and 90 mm. 



In the 22 mm. embryo (fig. 1) the root of the nerve enters the 

 brain at the ventral (rostral) end of the fissura prima (His). 

 The root fibers are traceable for some distance caudally, i.e., 

 towai^d the anterior commissure. In figure 1 only the portion of 

 the nerve which contains ganglion cells has been modelled. The 

 elongated ganglion terminale extends rostrally along the medial 

 side of the root of the olfactory nerve and continues for some 

 distance along the four primary branches into which the nerve 

 divides. From each of the free ends of the ganglion shown in 

 the model, strands of nerve fibers extend peripherally. In this 

 embryo the ganglion terminale is independent of the mass of 

 cells lying among the root bundles of the olfactory nerve known 

 to older authors as the 'olfactory ganglion.' In other embryos 

 the two masses of cells are frequently more closely related (fig. 5) . 

 The ganglion terminale may easily have been seen by earlier 

 workers and considered by them to be a part of the so-called 

 olfactory ganglion. The cells of the latter have the appearance 

 of neurilemma cells, being slender or flattened cells taking a 

 moderate stain in carmine. The cells of the ganglion terminale 

 have larger, more globular nuclei, are more closely packed and 

 take a deeper stain. 



The peripheral branches of the nerve in this 22 mm. embryo 

 pass down through the septum in several strands which end in 

 the wall of the vomero-nasal organ and in a small area of the 

 wall of the nasal sac immediately adjacent. 



The peripheral course of the nerve is much more readily fol- 

 lowed in sagittal sections. A model made from sagittal sections 

 of a 15 mm. embryo is drawn in figure 3. Here the root of the 

 nerve occupies the same position as in the previous embryo. 



