Harris, Joseph P., Jr.

English

Southern Methodist University

1949] DISAPPEARING RANGE PLANTS 115 placed by plants less palatable, not at all palatable, or even harmful to livestock. When little or no choice is given to the hungry animal, even the careful observer of livestock feeding on the range is misled in judging the palatability of species of range forage. As an example, the foliage of live oak and of sacahuiste is fed upon extensively during the winter months, while vir-tually untouched during the growing season. Similarly, the foliage of shin oak (available only during the growing sea-son), were it available during the winter months, might prove to be equally or more palatable than live oak. Some ranchmen, with thei:r ranges reduced largely to unpalatable forbs, on witnessing these efforts of their livestock to escape starvation, wrongly conclude that the plants upon which they feed are palatable. Close and accurate observation of livestock feeding on ranges less seriously depleted demon-strates that in the presence of better forage plants, these other plants are left untouched. Under continuous heavy g,raizing those plant species that are seriously reduced in numbers, or even eliminated, are good forage plants. It goes without saying that, on the other hand, those species that increase unduly under heavy grazing are poor or worthless as forage plants. To ensure benefits to range livestock, and thus contribute to Man's welfare, this trend towa:rds impov-erishment of the range must be reversed. Note FUSION 0F INTERNAL CAROTID ARTERIES IN THE DOGFISH, SQUALUS ACANTHIAS.--It is stated in the literature of vertebrate morphology that "the internal carotid arteries of Squalus acanthias fuse on enter-ing the carotid foramen. The internal carotids then separate (before giving off the lateral carotid 'efferent pseudobranchial' branches) and continue to form the Circle of Willis." I have, however, examined care-fully 200 individuals of this species to ascertain the disposition of the two branches of the internal carotid in the carotid foramen. My results showed that the degree of fusion was highly variable; that this fusion varied from being little more than a filamental connective between the carotid trunks (12 specimens) to a condition of fairly broad fusion (one specimen.) The short branch-arteries connecting the two carotids were usually of smaller diameter than the carotid trunks. In all of my specimens the right post-cranial carotid artery crossed ventral to the left, and supplied with blood structures on the left side of the brain. Conversely, the left post-cranial carotid artery crossed dorsal to the right, and supplied structures on the right side of the brain.-Jos-EPH P. HARRIS, JR., Assistant Professor of Biology, Southern Methodist University, Dallas. 

Fusion 0f Internal Carotid Arteries In The Dogfish, Squalus Acanthias

https://scholar.smu.edu/cgi/viewcontent.cgi?article=1194&context=fieldandlab

Fusion 0f Internal Carotid Arteries In The Dogfish, Squalus Acanthias

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Southern Methodist University