Lawrence Edmonds Griffin

“ While the Wolffian duct is the duct of the kidney, and is joined by tubules of the anterior part of the kidney, it is so modified in the male that its principal function is to serve as the duct of the testis, a vas deferens. The collecting tubules of the posterior part of the kidney join to form a urinary duct which is independent of the Wolffian duct. The posterior end of the Wolffian duct is straight and considerably expanded, forming a large seminal vesicle. The duct becomes more and more closely convoluted as it passes forward, and the kidney tissue overlying it diminishes. ”

“ The mouth and pharynx can be studied to better advantage later with the dissection of portions of the vascular system.
The oesophagus can be seen above the liver, by pressing that organ aside, as a somewhat constricted tube entering the anterior end of the abdominal cavity. It immediately joins the stomach, which is more or less expanded according to the amount of food contained in it. ”

“ In the midline of the body are two triangular dorsal fins, each attached to the body for about half its length. The basal portion of each is thick and muscular, and contains supporting cartilages embedded in the muscles. The remainder of the fin is flexible and semi-transparent, horny fin-rays being faintly visible between the layers of skin. In front of each fin is a strong spine which seems to serve both as a cutwater and a weapon of defense. (Eugaleus has no spines.) ”

“ By cutting away the cartilage dorsal to the nasal sac its base will be exposed, and the olfactory bulb will be shown to be closely adherent to a considerable part of the postero-dorsal surface of the organ. Numerous short nerves can be demonstrated to pass from the olfactory bulb into the olfactory organ; all these nerves together are considered as the first cranial or olfactory nerve. ”

“ The “dogfish” of inland waters belongs to an entirely different group. Two species of sharks are caught in numbers and used in laboratory work, the “spiny dogfish” (Squalus acanthias) and the “smooth dogfish” (Eugaleus galeus) . The first is easily distinguished by the sharp spine in front of each dorsal fin. Squalus acanthias is often referred to under the synonym Acanthias vulgaris, while Eugaleus galeus is more frequently named either Mustelus canis or Galeus canis. ”

“ Take notice of the following nerves, in order to ensure their preservation until the time comes to trace them more completely. A large nerve crossing the medial side of the orbit, the superficial ophthalmic; a nerve leaving the cranium opposite the optic lobe, passing under the superficial ophthalmic to the anterior muscle of the eyeball, the trochlear; several long ciliary nerves passing to the eyeball; several other nerves visible in the deep angle of the orbit.
Six muscles move the eye. Four of these arise close together at the deep postero-medial angle of the orbit. ”

“ If a large head is to be used especially for the dissection of the cranial nerves, only the brain, eye and ear need be studied in the present specimen. But in most cases it will be found best for the student to dissect the first dogfish as thoroughly as possible, working out the cranial nerves as well as the brain, and reserving the second head for a thorough review of the entire nervous system. ”

“ THE SKELETON There seems to be no easy way of cleaning the skeleton of dogfish which have been preserved in formalin or alcohol, the only procedure being to cut, pick, and scrape the flesh away from the skeleton. ”

“ Remove the ventral portions of the first and second superficial constrictors and clear the mass of muscles lying between the coracoid portion of the pectoral girdle and the mandible. Immediately in front of the girdle are two large muscles, the coraco-arcuales communes, whose fibres run inward and forward. These muscles cover the ventral surface of the pericardium, to the wall of which their median fibres are attached, while the lateral fibres are attached around the ventral ends of the gill arches. ”

“ The anterior surface of the olfactory lobe fills a large foramen in the anterior wall of the cranium and is pressed closely against the posterior surface of the nasal sac. Numerous small nerves, collectively forming the olfactory nerve, arise from the anterior face of the lobe, penetrate the membraneous wall of the olfactory organ, and are distributed to its highly folded surface. ”

“ Several sizes of dogfish are furnished by dealers. We consider it best to purchase large, fully developed specimens. The small specimens may be a little more convenient to handle, but the large ones have the important advantage of being sexually mature, while blood vessels and nerves are dissected better in large than in small specimens. Also, a number of structures are very different in mature animals from their condition in young ones. ”

“ The roof of the diencephalon also is very thin and is frequently broken during the exposure of the brain. The cavity seen within the diencephalon is the third ventricle.
Stalked bodies arising from the antero-lateral angles of the cerebral hemispheres are the olfactory lobes. The portion of the brain including the cerebral hemispheres and the olfactory lobes constitutes the telencephalon.
Dissection of the internal ear. The structures composing this organ lie in the projecting cartilage at the side of the medulla (auditory capsule) . ”

“ The anterior wall of the spiracle is strengthened by two small, flat, vertical cartilages, probably homologous with the branchial rays of the gill arches.
The remaining five visceral arches differ little in their construction. Dorsally, each has a flat, sickle-shaped pharyngo-branchial cartilage attached to the vertebral column by fibrous bands. The pharyngo-branchials of the last two arches are fused. Ventrad to each pharyngo-branchial is an epibranchial cartilage. The next segment of each arch is formed by the ceratobranchial cartilage. ”

“ The posterior mesenteric artery leaves the aorta a little distance back of the lienogastric and passes to the rectal gland, rectum, and cloaca.
Free the kidney from the body wall along its outer edge and turn it up so as to expose its dorsal surface. Observe the numerous parietal arteries (going to the body wall) and renal arteries (to the kidney) , which spring from the dorsal aorta. Branches of the parietals also pass into the kidney. ”

“ The hyoid branch separates from the hyomandibular trunk at about the same level as the preceding nerves, and then passes, deep in the tissues, around the angle of the jaw to the ventral side where it is distributed to the superficial constrictor muscles. Several nerves pass from the hyomandibular trunk and the hyoid branch to the dorsal superficial constrictors. ”

“ The denticle consists of dentine, the spine being of a much denser structure than the base. The teeth and the large spines of the fins and claspers are also composed of dentine and may be considered as modified placoid scales. ”

“ Passing posteriorly and ventrad close to the right side of the stomach and reaching the gastro-hepatic omentum, it divides into two branches, the gastro-hepatic and anterior intestinal arteries. The first gives off a small hepatic artery to the liver 15and a large gastric artery to the cardiac limb of the stomach. The anterior intestinal artery supplies the pyloric limb of the stomach, the pancreas, duodenum, and right side of the large intestine. ”

“ In males, the vasa deferentia appear as slender, irregularly coiled white tubules lying near the medial border of the kidneys; they are much less conspicuous than the oviducts, especially in young males. ”

“ Remove the muscle and connective tissue from the vertebral column for a short distance anterior to the first dorsal fin. Care is required not to cut away small cartilages occupying the positions of ribs. ”