File:Biology of the vertebrates - a comparative study of man and his animal allies (1949) (20196019220).jpg

Title: Biology of the vertebrates : a comparative study of man and his animal allies
Identifier: biologyofvertebr00walt (find matches)
Year: 1949 (1940s)
Authors: Walter, Herbert Eugene, b. 1867; Sayles, Leonard Perkins, 1902-
Subjects: Vertebrates; Vertebrates -- Anatomy; Anatomy, Comparative
Publisher: New York : Macmillan Co.
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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49° Biology of the Vertebrates apart. At the stage of about the sixth or seventh week, when the legs are simply two stubs on the two sides of the cloaca (Fig. 408), an elevation, the genital eminence, tipped by a conical projection, the genital tubercle, appears just within the anterior margin of the cloacal opening. Around the genital opening there forms a pair of folds, the labio-scrotal folds, which are destined to become either the labia majora of the female or the scrotal sac of the male. Soon the genital tubercle elongates somewhat and a slit, the urogenital opening, develops along its ventral surface. The lateral margins of the slit elevate next to form a second pair of enclosing folds, the inner genital folds, or the future labia minora of the female. Pubic Symphysis
Text Appearing After Image:
Ductus !> Deferens % (L Pubic * v \\ Symphysis Anus Fig. 409. Sagittal diagram of female genitalia. Fig. 410. Sagittal diagram of male genitalia. In the male the genital eminence, with its projecting tubercle, elongates still more into the corpus spongiosum and the glans of the penis, the uro- genital slit meanwhile closing over to form the penile part of the urethra. The inner genital folds become the two corpora cavernosa, joining together side by side above the corpus spongiosum to complete the body of the penis, while the labio-scrotal folds draw down and grow together, forming the scrotal sac. The seamlike ridge, or raphe, along the midventral line of the scrotum in the adult, represents the line of fusion between these embryonic structures. In the female the genital eminence and the genital tubercle remain comparatively undeveloped in the form of the clitoris, while the urogenital slit expands into the vestibular entrance to the vagina, and the two sets of folds on either side shape up into the labia minora and the labia majora.

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