HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM OF THE WEDDELL SEAL. 157 



stained with eosin and clear. The intermediate portion is a typical syncytium of clear 

 protoplasm in which are embedded many large nuclei : colloidal substance occurs at 

 various points bordering on the anterior lobe (Plate II. C, and text-fig. 7, col.). 



No sinusoids are present in the intermediate portion, there being, however, cleft-like 

 spaces between the strands of the syncytium. At the upper part of the gland the 

 intermediate portion seems to pass insensibly into the anterior lobe in fact, almost 

 to blend with that lobe, and the above structure would thus lead to an inference 

 that the middle portion is a derivative of the front part of the anterior lobe, since 

 both these portions are syncytial in character. The posterior lobe (Plate II. D) is 

 made up of a large amount of neuroglia in which large nuclei occur (nuclei of 

 neuroglia cells), and also here and there small masses of colloid which are passing 

 through the lobe from the intermediate portion. The large vessels of the posterior 

 lobe (not sinusoids) are also occasionally seen to be filled with masses of colloid 

 in which are embedded small bi- or tri-lobed masses which are either leucocytes or 

 degenerating nuclei from the intermediate portion. 



EXPLANATION OF PLATES. 



PLATE I. 



Serial sections of the medulla oblongata, pons, and mid-brain (Leptonycliotes weddellii). 



1 . At the decussation at the pyramids : 



S.G.R. Substantia gelatinosa Rolandi. 



n.c. Nucleus cuneatus. 

 n.g. Nucleus gracilis. 

 py.'l. Pyramidal decussation. 



2. Just above the pyramidal decussation : 



Pi/. Pyramids. 



Other lettering as in 1. 



3. At the lower region of the olivary body : 



C.R. Corpus restiforme. 



/. Tract of the fillet. 



o.n. Olivary nucleus. 



.< a. Superficial arcuate fibres. 



p.l.b. Posterior longitudinal bundle. 



. XII. Nucleus of 12th cranial nerve. 



n. X. Dorsal nucleus of 10th cranial nerve. 



4. At the mid-olivary region : 



i.a. Internal arcuate fibres, 

 n. IX. Nucleus of the 9th cranial nerve. 

 n.d. Part of Deiter's nucleus. 



(ROT. soc. EDIX. TRASS., 



X. and XII. Issuing fibres of the 10th and 



12th cranial nerves. 

 Other letters as iu preceding 

 figures. 



5. At the upper olivary region : 



IX. and VIII. Issuing fibres of the 9th and 8th 



cranial nerves. 

 a.n. Arcuate nuclei. 



6. Across the lower pontine region : 



'. 4- Cavity of the 4th ventricle. 

 VII. and VIII. Issuing fibres of 7th and 8th cranial 



nerves. 



D. VII. Nucleus of 7th cranial nerve. 

 p.n. Pontine nuclei. 

 f.p. Pontine fibres. 

 f.r. Formatio reticularis. 

 s.o. (?) Superior olivary nuclei. 

 bi. Trapezium. 



7. Across the middle of the pons : 



n. V. Nucleus of 5th cranial nerve (motor 

 nucleus). 



VOL. XLVIII., 865.) 



