Title: Bulletin
Identifier: bulletin7073sout (find matches)
Year: 1971- (1970s)
Authors: Southern California Academy of Sciences
Subjects: Science; Natural history; Natural history
Publisher: Los Angeles, Calif. : The Academy
Contributing Library: New York Botanical Garden, LuEsther T. Mertz Library
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden

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1973 KI:S1:,M« II No 11 ', THE OS TRANSILIENS IN FOUR SPECIES OF TORTOISES, CJENUS GOPHERUS Ray (1959), firsl Found a heterotropic or sesmoid bone, ihc os transiliens, in a chelonian, Gophwus polyphemus, Legler (1962) discovered tlie presence of the os transiliens in Gopherus agassizi and Go- pherus flavomarginatus. Ray (1959) showed histologically thai the os transiliens in Gopherus polyphemus was bone and not calcified cartilage, Differential stains of toluidine blue (for cartilage) followed by alizarin red S (for bone) were carried out on a series of 20 os transiliens taken from Gopherus agassizi and Gopherus ber- landieri (Evans, 1949; Willey, 1969). X-rays were taken of the os transiliens and com- pared to known samples of bone ami cartilage in Gopherus agassizi as a cbeck upon the determination of the presence of bone. A General Electric model 11AA-3A X-ray machine was used at 40 KVP and 50 milliamps using Kodak Industrial type M-2 X-ray film. Carapace length, skull length, and length and width of the os transiliens were measured on nine Gopherus agassizi, one Gopherus polyphemus, and two Gopherus berlandieri. Skull length was measured in a straight line from the anterior extremity of the snout to the tip of the supraoccipital crest with the skull resting on the articulated mandible. The greatest width and length of the os transiliens were measured. The length of the carapace was measured along the midline between vertical axes erected at the posterior border of the supracaudals and the anterior border of the nuchal. The movement of the os transiliens was examined on seven thawed and two live Gopherus agassizi, using a wire and x-ray analysis technique developed by Inman (1947). The os transiliens is a prow-shaped bone in the aponeurosis of the M. adductor mandibularis externus and is articulated in a joint capsule with a facet formed by the quadrate and prootic bones, the pro- cessus trochlearis oticum (Gaffney, 1972). This facet places the os transiliens slightly higher on its inner surface and somewhat lower on its outer lateral sur- face. The os transiliens appears to provide a gliding or smooth motion for the fan-shaped aponeurosis of the M. adductor mandibularis externus over the edge of the superior temporal fossa where it passes ven- trally to an insertion on the mandibular coronoid process. The os transiliens of all adult Gopherus agassizi (15) showed positive stains for bone. Five juvenile Gopherus agassizi showed positive stains for cartilage suggesting a replacement of cartilage by bone with maturity. The differential staining technique also indicated the presence of a small bony os transiliens in one specimen of Gopherus berlandieri which is the first to be so noted. The x-rays confirmed the stain- ing data in all cases. •UP
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2 4 C SKULL LENGTH Icml Figure I. Skull length (cm) relative to the Icfl o: transiliens length (mm) in Gopherus agassizi (dol I Gopherus polyphemus (open circles), and Gopherus berlandieri (open squares). The relationship between the os transiliens and skull length for Gopherus agassizi was found by the method of least squares to be Y=1.42X—1.18 and for Gopherus polyphemus to be Y = 1.85X-3.90. Ossification of the os transiliens occurs al a smaller size in Gopherus agassizi than has been found in Gopherus polyphemus (Fig. 1). The size of the os transiliens compared to carapace length in Gopherus agassizi (Fig. 2) shows that the larger tortoises have proportionally larger os transiliens (Table 1). In Gopherus agassizi the superficialis portion of the M. adductor mandibularis externus contracts and pulls on the broad part of the fan-shaped aponeurosis attached to the upper end or posterior portion of the os transiliens. This is adducted (inside the joint cap- sule) posteriorly on the process trochlearis pulling on the tendon attached in part to the front of the os III.' 5 15 25 CARAPACE LENGTH -CM Figure 2. Carapace length (cm) relative to length of the left os transiliens (mm) for Gopherus at. (dots), and a single specimen each of Go polyphemus (open circle), and Gopherus herh (open square). The relationship between the o carapace length for Gopherus agassizi was found using the method of least squares. The relations Y = 0.259X + 0.3?.

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