Distribution of carotid body type I cells and other periadventitial type I cells in the carotid bifurcation regions of the cat.

The bilateral distribution of carotid body type I cells was investigated in five non-pedigree cats by serially sectioning the carotid bifurcation regions. Carotid body type I cells occurred bilaterally in close proximity to the wall of the occipital artery or one of its proximal branches, and less frequently the ascending pharyngeal artery within a division of connective tissue with definable but irregular borders. Caudally, and separate from the principal mass of carotid body type I cells, isolated groups of periadventitial type I cells were found in seven out of ten specimens lying freely in the connective tissues around the occipito-ascending pharyngeal trunk and the origin of the occipital artery immediately rostral to the carotid bifurcation. Periadventitial type I cells were not observed at the level of the carotid bifurcation but on one occasion these cells were noted caudal to the carotid bifurcation lying adjacent to the wall of the rostral end of the common carotid artery. From our data on four specimens, reconstructions were made of the carotid body. The occurrence and significance of the periadventitial type I cells is discussed.