No abstract

No abstract

No abstract

Examination of the cardiac anatomy of lizards of the family Varanidae revealed that much of the previous literature contained basic errors both in description and interpretation. These are corrected and terminology of various authors is standardized.The varanid ventricle is similar to that of most other lizards in not being elongated, in having the base at right angles to the longitudinal axis, and in having the vertical septum weakly developed. However, it is not a typical lacertilian heart in that it has a number of characteristic ophidian features such as a muscular cone surrounding the cavum latero-dorsale and a prominent twisting of the cava. It lacks a gubernaculum cordis and a cartilaginous rod in the septum aortico-pulmonale, both of which are present in many non-varanid lizards, but seldom occur in snakes. The location of the heart is more posterior in the body than is true of other lizards.During preliminary investigations on reptilian cardiac physiology, it became apparent that there exists no clear understanding of basic squamate heart anatomy requisite for interpretation of experimental results. Sources of confusion have been ( 1 ) failure to standardize terminology and inconsistent and incorrect usage of terms, (2) improper orientation of materials, slides and/or drawings being examined or presented up-side-down and misinterpreted accordingly, and ( 3 ) an uncritical following of the mistakes of previous authors. Webb ('69) presented a partial review of the literature, standardized terminology, and by re-examining hearts of the species upon which much of the anatomical literature is based, corrected many previous errors. A series of papers, of which this is the first, expands and revises that study. The present one treats the ventricle of the lizards of the family Varanidae. This family was selected first, because: (1) It belongs to a group (Platynota) claimed to be ancestral to the ophidian line (but see reviews by Bellairs and Underwood '51, McDowell and Bogert '54), so that an understanding of the anatomy of varanids J. MORPH., 134: 335-350. may be important for phylogenetic interpretations. ( 2 ) Much of the previous literature has been based on this family and correction of previous erroneous interpretations of varanid cardiac anatomy also clears up a number of problems related to the general structure of the squamate heart. ( 3 ) The varanid heart has been used as a "typical" squamate heart (see Literature below). This unwarranted assumption must be disposed of before proceeding with further comparative studies.The ventricle is emphasized because most of the confusion in the literature centers around this part of the heart. THE GENERALIZED SQUAMATE VENTRICLEThe ventricle is typically conical with the apex directed posteriorly. In most lacertilians, it lies in the midline of the body with the bulbar region facing ven- 335