Erectile Tissue
The erectile tissue consists of two components as follows. There are marked species differences in regard to their structure and relative size.
15.2.1 Corpus spongiosum penis
This is a sleeve of erectile tissue that encloses the urethra from the pelvis to the distal extremity of the penis.
It is expanded distally as the glans penis and near the pelvis as the bulb of the penis (urethral bulb).King’s Applied Anatomy of the Abdomen and Pelvis of Domestic Mammals, First Edition. Geoff Skerritt. © 2022 John Wiley & Sons Ltd. Published 2022 by John Wiley & Sons Ltd.
Companion website: www.wiley.com/go/skerritt/abdomen
15.2.2 Corpus cavernosum penis
This erectile tissue is attached bilaterally to the left and right ischiatic tuberosities of the pelvis. It comprises a pair of fibrous cylinders that converge distally to form a single corpus cavernosum penis that lies dorsal to the urethra and extends distally to the end of the penis. This description is accurate for most species but does not apply to the dog (see Section 15.5.5).
The composition of the erectile tissue of the corpus cavernosum penis varies with the species. In man and the horse, it consists largely of smooth muscle with large cavernous spaces; this is the musculocavernous type of penis. The fibroelastic type, comprising fibrous and elastic tissue with small cavernous spaces, is found in the pig and the ruminants. During erection the release of neurotransmitters results in dilation and relaxation of the vascular components of the erectile tissue. Contraction of both the ischiocavernosus and bulbospongiosus muscles then blocks the escape of the increased blood flow, resulting in hardening of the penis, or tumescence.
During erection the musculocavernous type of penis increases greatly both in length and diameter. The fibroelastic penis undergoes straightening of the S-shaped bend in the body of the penis, the sigmoid flexure.
15.3