182:. Relative to the primitive protrogomorphous condition, the superficial masseter remains unchanged. The lateral masseter has shifted forward and upward, behind and medial to the superficial masseter. Here it originates from a wide zygomatic plate developed on the anterior (maxillary) root of the zygomatic arch. This shift of origin changed the direction of pull of the anterior part of the lateral masseter from 30 to 60 degrees, greatly strengthening the forward component of the masseter contraction.
191:
254:
147:
25:
291:
Myomorphs combine characteristics found in both the sciuromorphous and hystricomorphous rodents. Both the lateral and medial masseter muscles have migrated, and both a large zygomatic plate as well as a large infraorbital foramen are present. This type gives the greatest anteroposterior component of
244:
In hystricomorphs the medial masseter is enlarged and originates on the side of the rostrum (in extreme cases as far forward as the premaxilla), where it then passes through a greatly enlarged infraorbital foramen to insert on the mandible. This gives an almost horizontal resultant to the muscle
94:
of the skull. The anteroposterior or propalinal (front-to-back) motion of the rodent jaw is enabled by an extension of the zygomatic arch and the division of the masseter into a superficial, lateral and medial muscle. The four main types are described as protrogomorphous, sciuromorphous,
138:. The lateral masseter inserts here as well and originates from the lateral portion of the zygomatic arch. The small medial masseter originates along the medial surface of the zygomatic arch and inserts along the dorsal portion of the mandible at the end of the tooth row.
103:
The members of this grade include nearly all of the pre-Oligocene rodents of North
America and Asia and some of those of Europe. Several lineages survive into the Oligocene or early Miocene, with only one species still alive today, the
313:
Aplodontid, Scuirid, Castorid, Zapodid and
Geomyoid rodents of the Rodent Hill locality, Cypress Hills Formation, Southwest Saskatchewan, Master of Science thesis, Geological Sciences
288:
may have allowed for the passage of the masseter muscle. If true, this subfamily would represent an additional example of myomorphy in the rodent suborder
Sciuromorpha.
436:"Evolution of the zygomasseteric construction in Rodentia, as revealed by a geometric morphometric analysis of the mandible of Graphiurus (Rodentia, Gliridae)"
224:
43:
285:
122:) are considered secondarily protrogomorphous since their zygomatic condition is clearly derived from a hystricomorphous ancestor. The
61:
280:: in the latter it is often referred to as pseudomyomorphy). suggest that the infraorbital foramen of the extinct
473:
292:
any rodent zygomasseteric system, which might explain the success of the cosmopolitan
Muroidea.
151:
39:
311:
127:
8:
198:
demonstrating the hystricognathous lower jaw and hystricomorphous zygomasseteric system.
405:
362:
345:
452:
435:
409:
130:
is small. The superficial masseter originates on the lateral surface of the anterior
123:
447:
434:
Hautier, Lionel; Michaux, Jaques; Marivaux, Laurent; Vianey-Liaud, Monique (2008).
397:
357:
207:
110:
105:
87:
478:
203:
155:
91:
401:
467:
16:
Bones & muscles in rodents' heads that enable them to chew front-to-back
277:
238:
167:
119:
233:
215:
179:
171:
269:
211:
190:
163:
253:
273:
265:
229:
219:
175:
135:
134:
and inserts along the ventral margin of the angular process of the
433:
281:
131:
115:
257:
195:
146:
83:
388:
384:
Korth, William W.; Emry, Robert J. (1991). "The skull of
154:. Note the classic sciuromorphous shape of the anterior
162:
This condition is found in most members of the family
34:
may be too technical for most readers to understand
379:
377:
375:
373:
202:This condition is found throughout the suborders
465:
228:). Hystricomorphy is also found in the African
126:of protrogomorph rodents is unmodified and the
370:
429:
427:
425:
423:
421:
419:
416:
339:
337:
335:
333:
331:
260:skull displaying the myomorphous condition
451:
440:Zoological Journal of the Linnean Society
383:
361:
62:Learn how and when to remove this message
46:, without removing the technical details.
252:
189:
145:
328:
316:. Saskatoon: University of Saskatchewan
466:
86:is the anatomical arrangement of the
44:make it understandable to non-experts
343:
309:
237:, which is a member of the suborder
18:
302:
95:hystricomorphous, and myomorphous.
13:
363:10.1111/j.1558-5646.1965.tb01696.x
14:
490:
346:"Grades and Clades Among Rodents"
214:, it is found in the superfamily
185:
98:
453:10.1111/j.1096-3642.2008.00453.x
23:
264:This condition is found in the
141:
170:), and also in members of the
1:
295:
248:
7:
10:
495:
402:10.1017/S0022336000033291
344:Wood, Albert E. (1965).
80:zygomasseteric structure
390:Journal of Paleontology
152:oriental giant squirrel
310:Bell, Sean D. (2004).
261:
199:
159:
256:
193:
149:
76:zygomasseteric system
128:infraorbital foramen
210:. In the suborder
90:of the jaw and the
262:
200:
160:
72:
71:
64:
486:
458:
457:
455:
431:
414:
413:
381:
368:
367:
365:
341:
326:
325:
323:
321:
306:
218:and some fossil
67:
60:
56:
53:
47:
27:
26:
19:
494:
493:
489:
488:
487:
485:
484:
483:
464:
463:
462:
461:
432:
417:
382:
371:
342:
329:
319:
317:
307:
303:
298:
251:
225:Pappocricetodon
208:Anomaluromorpha
188:
144:
111:Aplodontia rufa
106:mountain beaver
101:
88:masseter muscle
68:
57:
51:
48:
40:help improve it
37:
28:
24:
17:
12:
11:
5:
492:
482:
481:
476:
474:Rodent anatomy
460:
459:
446:(4): 807–821.
415:
396:(6): 984–994.
369:
327:
300:
299:
297:
294:
250:
247:
245:contraction.
204:Hystricomorpha
187:
186:Hystricomorphy
184:
143:
140:
100:
99:Protrogomorphy
97:
92:zygomatic arch
70:
69:
31:
29:
22:
15:
9:
6:
4:
3:
2:
491:
480:
477:
475:
472:
471:
469:
454:
449:
445:
441:
437:
430:
428:
426:
424:
422:
420:
411:
407:
403:
399:
395:
391:
387:
380:
378:
376:
374:
364:
359:
355:
351:
347:
340:
338:
336:
334:
332:
315:
314:
305:
301:
293:
289:
287:
283:
279:
275:
271:
267:
259:
255:
246:
242:
240:
236:
235:
231:
227:
226:
221:
217:
213:
209:
205:
197:
192:
183:
181:
177:
173:
169:
165:
157:
153:
148:
139:
137:
133:
129:
125:
121:
117:
113:
112:
107:
96:
93:
89:
85:
81:
77:
66:
63:
55:
45:
41:
35:
32:This article
30:
21:
20:
443:
439:
393:
389:
385:
353:
349:
318:. Retrieved
312:
304:
290:
286:Cedromurinae
278:Sciuromorpha
263:
243:
239:Sciuromorpha
232:
223:
201:
168:Sciuromorpha
161:
150:Skull of an
142:Sciuromorphy
120:Bathyergidae
109:
102:
79:
75:
73:
58:
49:
33:
356:: 115–130.
320:10 February
272:) and most
194:Skull of a
468:Categories
296:References
284:subfamily
234:Graphiurus
216:Dipodoidea
180:Geomyoidea
178:, and the
172:Castoridae
166:(suborder
410:132211896
350:Evolution
270:Myomorpha
249:Myomorphy
222:(such as
212:Myomorpha
164:Sciuridae
156:zygomatic
52:July 2017
386:Cedromus
274:Gliridae
266:Muroidea
230:dormouse
220:Muroidea
176:Eomyidae
136:mandible
118:(family
116:molerats
282:sciurid
158:region.
132:maxilla
124:rostrum
114:). The
84:rodents
38:Please
408:
258:Gerbil
196:nutria
174:, the
479:Skull
406:S2CID
82:) in
322:2017
308:{*
206:and
78:(or
74:The
448:doi
444:154
398:doi
358:doi
42:to
470::
442:.
438:.
418:^
404:.
394:65
392:.
372:^
354:19
352:.
348:.
330:^
241:.
456:.
450::
412:.
400::
366:.
360::
324:.
276:(
268:(
108:(
65:)
59:(
54:)
50:(
36:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.
