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

The bilateral distribution of carotid body type I cells was investigated in 5 mongrel dogs and compared with the arrangement of type I cells in beagles by serially sectioning the carotid bifurcation regions. The distribution of type I cells was not affected by the pedigree of the dogs. In both mongrel dogs and beagles type I cells were arranged in close proximity to the wall of the ascending pharyngeal artery within a division of connective tissue with defineable but irregular borders. Occasionally, type I cells were observed in relation to the occipital and external carotid arteries. This association of type I cells and connective tissue formed the principal mass of the carotid body. Caudally, and separate from the principal mass, isolated groups of periadventitial type I cells lay freely in the connective tissue adjacent to the internal and external carotid arteries in both mongrel dogs and beagles. Less commonly, and in mongrel dogs only periadventitial type I cells were noted alongside the carotid bifurcation and the rostral end of the common carotid artery. Three-dimensional reconstructions of the distribution of carotid body type I cells and periadventitial type I cells from the left and right carotid bifurcation regions were made. In all specimens rostral-caudal dimensions of the distribution of carotid body type I cells and periadventitial type I cells were recorded and compared bilaterally.