Part 218

The =sympathetic system= of the pig has received very little attention from anatomists. The =superior cervical ganglion= is long and fusiform. It gives off filaments which join the vagus near the ganglion nodosum. The =cervical trunk= is short and relatively larger than in the ox; it is inclosed in a common sheath with the vagus in the neck and separates from that nerve to join the =middle cervical ganglion= at the thoracic inlet.

THE NERVOUS SYSTEM OF THE DOG

The =spinal cord= is almost circular in cross-section except at the well-marked cervical and lumbar enlargements, where it is compressed dorso-ventrally. The conus medullaris lies over the junction of the sixth and seventh lumbar vertebræ. The length of the cord of a rather large dog was found to be about 38 cm.; of this, the cervical part was 11 cm., the thoracic 17.4 cm., the lumbar about 7 cm., and the sacro-coccygeal about 2.6 cm. (Flatau-Jacobson).

FIG. 539.—BASE OF BRAIN OF DOG.

a, Olfactory bulb; a′, a″, external and internal olfactory tracts; b, optic nerve; c, oculomotor nerve; d, trochlear nerve; e, trigeminus; f, abducens; g, facial; h, auditory; i, glosso-pharyngeal; k, vagus; l, spinal accessory; m, hypoglossal; 2, trigonum olfactorium; 3, anterior perforated substance; 4, tuber cinereum and infundibulum; 4′, mammillary body; 5, pyriform lobe; 6, temporal lobe; 7, parietal lobe; 8, frontal lobe; 9, pons; 10, medulla oblongata; 11, cerebellum; 12, cerebral peduncle; 13, occipital lobe. (Ellenberger-Baum, Anat. d. Hundes.) ]

FIG. 540.—BRAIN STEM OF DOG, DORSAL VIEW.

a, Spinal cord; b, dorsal median groove; c, c′, funiculus gracilis; c″, clava; d, d′, funiculus cuneatus; d″, tuberculum cuneatum; e, funiculus lateralis; e′, tuberculum Rolandi; f, medulla oblongata; I, II, III, floor of fourth ventricle (fossa rhomboidea); g, limiting groove; h, median fissure; i, eminentia medialis; k, ala cinerea; l, l′, pons; m, posterior peduncle, and n, middle peduncle of cerebellum (cut); o, anterior peduncle of cerebellum; p, p′, corpora quadrigemina, anterior and posterior; q, q′, peduncles (brachia) of corpora quadrigemina; r, thalamus; s, massa intermedia; t, stria medullaris; u, anterior tubercle of thalamus; v, pulvinar; w, corpus geniculatum laterale; x, corpus geniculatum mediale. (After Ellenberger, in Leisering’s Atlas.) ]

The =brain= weighs about 60 to 70 g. in dogs of medium size, but there is, of course, a wide range of weight in the different breeds. Thus in small terriers the weight is 30 g. or even less, while in very large dogs it may exceed 150 g. It corresponds much more closely with the cranium in size and general form than in the animals previously described; this is specially true of the small breeds, in which the bony crests and frontal sinuses are little developed.

The =medulla= is broad and thick. Its ventral surface is strongly convex from side to side. The pyramids are large and prominent and are limited by distinct median and lateral grooves. The olivary eminence is a well defined oval elevation situated between the pyramid and the superficial origin of the hypoglossal nerve. The external arcuate fibers form a wide band which crosses the lateral surface obliquely upward and forward, and obscures the groove which limits the restiform body externally. The cuneate tubercle is distinct. The rhomboid fossa is deep and narrow.

FIG. 541.—PART OF CROSS-SECTION OF BRAIN OF DOG, PASSING THROUGH GANGLION HABENULÆ.

Al, Ansa lenticularis of thalamic radiation; C a d, dorsal end of hippocampus; C a v, ventral end of same; C c, corpus callosum; C g m, corpus geniculatum mediale; C m, corpus mammillare; F i d, fimbria; F i v, ventral part of fimbria; G h, ganglion habenulæ; M B, fasciculus retroflexus; P p, pes pedunculi; T h, thalamus; T o, tractus opticus; T t, habenula; V A, fasciculus thalamo-mammillaris; V F, fornix ventralis; II, lateral ventricle; III, third ventricle. (After Probst.) ]

The =pons= is relatively small. The =corpus trapezoideum= is very wide and is divided by the pyramids into two lateral parts. The =cerebellum= is very broad, but is low and also compressed from before backward. Rather more than half of it is overlapped by the cerebral hemispheres. The anterior surface is accurately adapted to the concave tentorial surfaces of the hemispheres and to the posterior corpora quadrigemina and their commissure. The posterior surface is almost vertical and is convex centrally and flattened laterally. The vermis is prominent and in general well defined, although it is connected in its middle part with the hemispheres. The latter are three-sided and consist of four lobules. The anterior peduncles are very short.

The =posterior corpora quadrigemina= are large, very wide apart, and prominent, and are connected by a curved commissure. The =internal geniculate body= is large. In the deep interpeduncular fossa are two small bands which indicate the course of the fasciculi retroflexi, tracts which connect the habenular and interpeduncular ganglia. The =mammillary body= is double. The =tuber cinereum= is relatively large. The =pituitary body= is circular and rather small.

The =cerebral hemispheres= are very broad behind and diminish in width anteriorly; there is a sudden narrowing at the frontal poles, which are flattened laterally. The tentorial surfaces are concave and form a deep cavity which receives the anterior part of the cerebellum. The arrangement of the fissures and gyri is simpler than in the animals previously examined. The chief fissures are as follows:

1. The =lateral fissure= (of Sylvius) extends upward and backward from the sulcus rhinalis a little behind the middle of the lateral surface of the hemisphere.

2. The =ectosylvian fissure= has approximately the shape of an inverted u, and curves over the lateral fissure. It is regarded as consisting of three parts—anterior, middle, and posterior (F. ectosylvia anterior, media, posterior).

3. The =suprasylvian fissure= lies above and approximately concentric with the preceding. It also consists of three parts—anterior, middle, and posterior.

4. The =ectomarginal= or =collateral fissure= runs forward on the dorsal aspect of the hemisphere almost parallel with the dorso-medial border. A little in front of the middle of the surface it gives off a short =ansate fissure= (F. ansata) which runs obliquely inward and forward, and is continued by the coronal fissure.

FIG. 542.—CEREBRUM OF DOG, DORSAL VIEW.

a, End of lateral fissure (of Sylvius); b, ectosylvian fissure; c, c′, c″, suprasylvian fissure; d, fissura ansata minor; e, ectolateral fissure; f, ectomarginal or collateral fissure; g, fissura ansata; h, coronal fissure; i, medilateral fissure; k, entomarginal fissure; l, postcruciate fissure; m, cruciate fissure; o, presylvian fissure; p, fissura prorea. (After Ellenberger, in Leisering’s Atlas.) ]

FIG. 543.—FISSURES OF LATERAL SURFACE OF CEREBRUM OF DOG, RIGHT SIDE.

a, Fissura prorea; b, frontal fissure; c, olfactory fissure; d, d′, sulcus rhinalis; e, presylvian fissure; f, precruciate fissure; g, postcruciate fissure; h, cruciate fissure; i, lateral fissure (of Sylvius); k, k′, k″, suprasylvian fissure; l, l′, l″, ectosylvian fissure; m, fissura ansata minor; n, ectomarginal or collateral fissure; o, fissura ansata; p, coronal fissure; q, ectolateral fissure; r, medilateral fissure; s, entomarginal fissure. (After Ellenberger, in Leisering’s Atlas.) ]

FIG. 544.—RIGHT CEREBRAL HEMISPHERE OF DOG, INNER SIDE.

1, Corpus callosum; 1′, genu, 1″, splenium of corpus callosum; a, genual fissure; b, splenial fissure; c, suprasplenial fissure; d, hippocampal fissure; e, sulcus corporis callosi; f, postsplenial fissure; g, lesser cruciate fissure; h, cruciate fissure. (After Ellenberger, in Leisering’s Atlas.) ]

5. The =coronal fissure= is the continuation of the ectomarginal. It runs forward and downward, curving around the cruciate fissure, and ends behind the middle of the presylvian fissure.

6. The =ectolateral fissure= lies between the posterior part of the ectomarginal fissure and the suprasylvian fissure.

7. The =entomarginal fissure= lies between the anterior part of the ectomarginal fissure and the dorso-medial border. It is often indistinct and not rarely absent.

8. The =presylvian fissure= begins at the sulcus rhinalis, a little in front of its middle, and curves over the anterior third of the lateral surface of the hemisphere in front of the coronal fissure.