HISTOLOGY OF THE CENTRAL NERVOUS SYSTEM OF THE WEDDELL SEAL. 865 
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. 
Puate I. 
Serial sections of the medulla oblongata, pons, and mid-brain (Leptonychotes weddelliz). 
1. At the decussation of the pyramids: X. and XII. Issuing fibres of the 10th and 
12th cranial nerves. 
Other letters as in preceding 
figures. 
S.G.R. Substantia gelatinosa Rolandi. 
n.c. Nucleus cuneatus. 
n.g. Nucleus gracilis. 
py-1. Pyramidal decussation, 5, At the upper olivary region : 
IX. and VIII. Issuing fibres of the 9th and 8th 
cranial nerves, 
a.n. Arcuate nuclei. 
2. Just above the pyramidal decussation : 
Py. Pyramids. 
Other lettering as in 1. 
6. Across the lower pontine region : 
3. At the lower region of the olivary body : J Carvey oe she sels ventric 
ea Ce ventricle. 
C.R. Corpus restiforme. VII. and VIII. Issuing fibres of 7th and 8th cranial 
f. Tract of the fillet. nonves 
o.n. Olivary nucleus. D. VII. Nucleus of 7th cranial nerve. 
s.a. Superficial arcuate fibres. p.m. Pontine nuclei. 
p.l.b. Posterior longitudinal bundle. fp» Pontine fibres. 
n. XII. Nucleus of 12th cranial nerve. fr. Formatio reticularis, 
n. X. Dorsal nucleus of 10th cranial nerve. s.o. (2) Superior olivary nuclei. 
4, At the mid-olivary region: bt. Trapezium. 
i.a. Internal arcuate fibres. 7. Across the middle of the pons : 
n. [X. Nucleus of the 9th cranial nerve. n. V. Nucleus of 5th cranial nerve (motor 
n.d. Part of Deiter’s nucleus. nucleus). 
TRANS. ROY. SOC. EDIN., VOL. XLVIIL, PART IV. (NO. 31). 127 
